As artists we are regularily asked to donate art, and every artist has to make decisions to donate or not to donate. For me the criteria is simple:
1. If I were wealthy would I donate generously to this cause?
2. If I had the time would I donate 20, 30 or 40 hours to this cause?
If the answer is yes to both then I am happy to donate a painting. If I spent 40 hours stuffing envelopes to help a cause, why not spend those 40 hours painting (lots more fun!!) and then donate the results to the cause? Call me crazy but I think painting is more fun than menial labor, and if my painting can bring them in a fair amount then it is worth more to them than me with the enevelopes.
Once the decision to donate is made -- and I make it purely on the basis of the criteria I have mentioned -- then consider the potential benefits. I say potential because there is no guarantees this will happen, but it is possible your art will advertise itself through your donation. You may gain publicity, recognition or even sales from that donation. So you help a cause you believe in, enjoy the process, and get some possible business help in the process -- what could be better?