I would definitely be less-inclined to make monetary and material donations without being compensated. With the 1.2 kids I have now, I have to make sure that they are taken care of, along with my wife.
There are some things that I have donated without expecting reward, like some old costume items which I was never going to use again. However, seeing as how they were not of use to me, I was not losing value by donating them, but gaining value added to my LARPing experience. I have also donated cash to a couple chapters and items to the Traverse City auction. It is highly unlikely that I would have gone through that trouble without some kind of compensation.
Now, I may have accepted in-game compensation for my character or some kind of personal Plot or something (if at my local chapter), rather than Goblin Stamps; but I see Gobbies as a great way for the return on your donation investment to be standardized.
Everyone knows what they're going to get from a particular donation and everyone gets the same benefits from spending those points that they earn (monthly/event blankets, production, coin, etc.). In this way, there is no argument of "Well, his Plot arc was cooler and more involved than mine." or "He got a better MI in-game because of his donations and I got this crappy mace that I don't even have the skill to use!".
Donations of my time and sills, however, are a dfferent story. I am fairly generous with my own time and do not see it as burdensome to lend it to a needy cause. If there were no compensation for donations, I would still likely volunteer to help with things that I am skilled in: website stuff, cleaning, organizing, building (both foam and real construction, if the materials were provided), etc. Again, though, the Goblin Stamp system helps to provide a standard reward for everyone's time so that no one feels slighted and we can all donate on an even playing field.
-Luke