I plucked a few hairs from my chest, and now they've grown back thick and prickley. I'm sorry I plucked them now, b/c they look worse. Will the hair return to normal if I leave it alone for a few cycles of growth and regrowth?

Yes, they should. If you only have a few, you could get them zapped with electrolysis by a pro, or even try doing it yourself (which I don't recommend).

I'm 20, and I've always had a little bit of a uni-brow, and I started plucking about a year ago. Now when I leave it alone it seems to be thicker than before. Is that because plucked hairs grow back thicker and longer as a form of revenge?? or just because Im getting older and harrier? I don't want to make it any worse in the long run than it has to be, but I think I might be making it worse by plucking. what do you think?
...thank you so much!

Gabbo, it's because you're getting older and hairier. No revenge of the hairs!