Yeah, if people are not motivated to donate, trying to push them into it isn't likely to work.
Another side of it, I remember my Dad said he donated some money to the Reagan campaign in the 80's. It wasn't much, but in response he was slammed with so much junk mail trying to get him to donate more money, he figured they spent his entire donation sending junk mail back to him. However, I doubt people actually thinking of giving money to Obama now would have the sense to come to that conclusion.