I would like to suggest that, to the contrary of public opinion, happiness is not all that important.
First
 there is the question of what I mean when I say 'happiness'.  I mean 
that hedonistic sense of happiness, the 'opposite of what I feel when 
I'm depressed' happiness.  I do not mean the vaguely defined Aristotlean
 'eudaimonia'.
I have five loosely related arguments against happiness that I would like to present:
-Nozick's Experience Machine
-The Rocking Chair Test
-Choice Experiments
-Happiness' Running Average
-Marginal Utility
-Personal Growth
I will not present a clear-cut argument.  At 
most, these are just running hunches that I think could be expounded 
into a deeper argument somewhere in the future.
=Nozick's Experience Machine=
Nozick's famous thought experiment goes something like this:
1-Happiness is all that's important.
2-Suppose there is a giant box (a la Matrix) that will make you feel enumerable pleasure so long as you are hooked up to it.
3-By 1 and 2, you should just sit in the box and do nothing else and enjoy the rest of your life.
And
 the conclusion is something along the lines of, "Something doesn't feel
 right about this conclusion."  That's really all there is to this 
argument (I admit it is rather weak).
I've noticed that this argument is rather hit or miss.  Some people 
(a lot of people, in my experience) agree with me and say that surely 
this isn't _all_ there is to life.  However, some others (you might be 
one of them) say that, indeed, this is all there is to life.  To these 
people I would suggest you pull out as many loads as you can, go to the 
Projects in Chicago, buy as much heroin as you possibly can, and enjoy 
your though-box induced pleasure-coma (just time your supply right so 
you can die of an overdose right when your supply runs out).  (or, 
alternatively, read on to see if some other argument in this article 
catches your fancy)
I can give a rather personal account of this.  There was a Spring 
Break a long time back where I gathered all of my videogames and my 
internet, piled my pillows in a corner, and did not leave that spot.  I 
felt great.  I felt a hedonistic sense of pleasure and when I was done I
 was quite the opposite of depressed--but something else felt negative 
about the experience.
=The Rocking Chair Test=
Some people might counter, "Well, 
you're only considering pleasure in the short-term, because our 
interests change/etc., you need to take a longer view of happiness."  
Aside from me arguing that technically the experience machine (by virtue
 of the fact that it gives 'experiences' and by what the word 
'experience' entails) already covers this, I'd like to give a different 
personal account of how this might go wrong.
The rocking chair test asks us to view ourselves far in the future 
in a rocking chair--what will we think about what we are doing now?
I
 posit, despite my youth and naivety, that I have to some extent 
undergone this test.  Recalling back on my early childhood I have lots 
of memories--playing Earthbound, Chrono Trigger, and Secret of Mana.  
All videogames, and all give me a sense of 'pleasure' in reminiscing on 
them.
But again, something feels off--something doesn't feel quite right 
in the same way that something doesn't feel quite right in Nozick's 
thought experiment--and I hope to get to what this may be near the end 
of this article.
=Choice Experiments=
There is a TED speaker who has done some
 experiments on choice (citation needed).  In particular, one of her 
surveys with people who have lost loved ones interests me.  Because of 
some weird legal differences, in one country a medical decision was 
chosen by the doctors, and in the other by the loved ones.  In the 
country where the individual died and the loved ones had no choice in 
the matter, they reported that they were happy about the decision.  In 
the other country, they were upset by the decision and felt less happy 
_but would rather have made the decision anyways_.  This to me seems to 
be indicative that something else more important than just blanket 
happiness is occurring here.
=Happiness' Running Average=
There is another fairly famous 
study (citation needed) about paraplegics and lottery winners.  A few 
months after they surveyed how happy they were and the results were as 
you might expect.  Paraplegics reported depression and lottery winners 
reported being on top of the world.  However, a few years afterwards, 
they base-lined.  The paraplegics and lottery winners were about the 
same.
Similar studies have been done and they seem to report the same thing:  you can't be permanently happy, you'll always baseline.
(aside: 
 there are some interesting and decent methodological holes in these 
papers that have not been filled that one could reasonably bring up, and
 I admit that these translate as holes in my argument as well.  For 
example, one possible explanation is that an _absolute_ metric of 
happiness might catch that lottery winners end up permanently being 
happier; and that the problem with the study was that the people in the 
study in essence created a new higher standard baseline for happiness, 
so that their reported _relative_ happiness base-lined.  I have doubts 
about this explanation, but admit that it's a methodological hole.)
This means, even if I were wrong and happiness qua happiness were 
important, because I can't really be happy in the long-run anyways, 
there would be no major change in my behavior, in fact...
=Marginal Utility=
The optimal strategy would be to stay slightly depressed.
If 
it is the case that happiness runs under some running average metric, 
then a goal would be to avoid major depressive downswings.  All other 
strategies wouldn't make any major difference in overall long-run 
happiness (barring my math colleagues giving me some pathological 
function with higher-than average area).  If one were to stay slightly 
happy for a long-period of time, then eventually one would either end up
 depressed for a long-period of time, or go through a dramatic and 
possibly catastrophic depressive episode.  As such, it would make sense 
(again, only if the previous section is indeed true) to stay slightly 
depressed so that the only possible mood swings are positive ones, and 
so that you become somewhat acclimated to the average state.
=Growth=
All of the above are really just clues.  So far I've
 stated that there is something other than just blanket happiness that 
seems to be important, but have not given any example of what this may 
be.  Now, this is not a logical necessity.  I could express doubt at the
 hypothesis that pleasure qua pleasure is all that is important; and it 
would be up to the dissenter to provide evidence to the contrary.  That 
is, saying, "Well, what else could it be?"  Is not a valid argument (it 
is a logical fallacy, at most).
As such, even though I will present something (which you might have 
guessed given the title of this section), that doesn't mean that _this_ 
either is all inclusive.  That is, I will not claim that pleasure and 
this conclusive cover all areas.  Just that this is an important area 
that pleasure overlooks.
Moreover, my argument remains fairly weak.  I will point out the 
hole, but keep in mind that this too is just ultimately another hunch.
Using
 an argument by performative contradiction, one could argue against what
 I would nomer as 'total atrophins'.  That is, one can not say that one 
should atrophy in all possible senses, since in doing so one would 
indubitably have to be dead, and thus would not be able to make an 
argument for 'total atrophins'.  As such, one should not engage in 
'total atrophy'.
Now, it is a fallacy for me to thereby form the opposite of this, 
and say "Therefore, one should strive for 'total growth'."  However, in 
the same way that correlation does not imply causation; but gives a 
rather good hint, I think that this argument gives a fairly good hunch 
that such a statement might not be far off.  Even though, at this point,
 I can't rigorously show such a statement.