To be actually noticeable any upgrade has to lose you *a lot* of weight. If you can measure it in pounds you'll probably feel it..... if you are paying $1,000's extra to lose the weight of a paperclip - eh not so good an investment. I've always heard that it really is more beneficial to lose rotating mass than static weight (and I even saw an article recently, wish I could remember where..., that did some real world testing and confirmed it), but still it is definitely right to say the best way to be better at hills is to ride up hills.

Shaving grams will save you seconds.... unless you are racing and those seconds are vitally important then its not going to make too much of a difference to you. Anyway climbing never gets any easier - you just suffer faster