You're assuming that users don't vote up the questions on your proposal simply because they don't understand the importance of upvoting.
But the Area51 is the place mostly for more experienced users willing to start new sites. If the user don't understand the concept of voting, he/she wouldn't be valuable commiter anyway, so why care. On the other way, think more like that, that the users are aware on limited upvotes for proposal, and don't want to waste them on questions, which they don't find themselves interesting enough.
IMHO on define phase, the example questions are much more important than upvotes. Upvotes are the natural consequence of good example questions. Upvoting only to fulfill phase requirements is against the concept of the phase.