The whole concept of reputation in Area 51 is a bit wonky. We're not building a canon of Q&A knowledge here, so the very premise of awarding up-votes and reputation for "good contribution" is a bit forced — square peg, round hole.
All is well, though, at least for the time being. Most of the "proposal vetting" of Area 51 is handled through the discussion threads and flagging, and ultimately through end-user support for these proposal ideas. What I mean by that is, if a proposal is somehow "off," it will not get support and be "closed" anyway — I.e. cleaned up by the abandoned proposal process.
If a proposal is egregiously bad, flagging is a perfectly fine option. We'll take care of it. Also, keep in mind that when a proposal reaches about 45% commitment, that triggers a hands-on "review" of the proposal and its fitness and viability. So there is a bit of an editorial layer to make sure everything is going well when a proposal gets far enough along to be "of concern." Reading through the accumulated discussions between the followers is a big part of that process.
What I am saying is that it takes more to turn a site into a proposal than simply having it exist in Area 51. All the checks and balances we added over the years have augmented the community self-moderation. That largely makes up for the shortfalls in the current implementation.
Speaking of implementation, Area 51 is due for a next-generation upgrade. That's going to be a big project going into this year; to figure out how to make Area 51 work for a next generation of sites. That effort, more than anything else, is why I am not inclined to start kluging these band-aid fixes like changing the reputation requirements to close proposals.