You can rack up quite a few AP's taking only things you are interested in, or would have to take the regular version for anyway. I've taken 13 (exams at least, something like 9 or 10 classes), and none were "just to take an AP."
If you have a choice between regular and AP, choose AP, even if you don't care about the subject, as it will most likely be more interesting/fun anyway.
If you have a choice between an AP in a subject you hate and an AP in a subject you find interesting, take the latter.
If you have a choice between an AP in a subject you don't hugely care about and regular in a subject you love, go for regular in the subject you love.