I feel that we are forgetting an important issue here. Voting maintains the popularity of a given game's ranking on those websites where we make our vote. Its not just about how much Gold/Cubi we obtain, but whether we appreciate the owner/provider and staff enough to show it by voting.
So, while Donating is a nice plus for the Game Owners/Moderators, it should be considered as an extra, something we utilise only when we can responsibly afford to.
Voting should not simply be considered as an easy option to obtain in-game gold, but as a measure of our appreciation for the game in which we invest our enjoyment.