Unfortunately, the reputation model of the Stack Exchange Q&A does not map very well to the site-creation process of Area 51, so it's not really something you should expect to accumulate in the context of this site. We simply rely on a different model.
Proposals are meant to be developed by the audience who will actually use the site. Area 51 has increasingly discouraged 3rd-parties from asserting themselves as "expert site creators" across every idea proposed here.
The early users you linked above were more prolific because they were first to propose subjects closer to our original developer audience, but it hasn't been that way for a long time. Ultimately, it is up to each new community to administer and prove they have the support needed to turn their idea into a site.
To this day, I still get flags "objecting" to a proposal with reasons like:
- These don't look like Stack Exchange users
- The 'followers' don't have any experience or reputation
- I would never use this [site]
So no, I am not inclined to encourage a more prolific layer of "senior users" overseeing the early proposal process. There's just too much disconnect in what a typical 10K user should reasonably do. Area 51 is not like your typical Stack Exchange collection of knowledge meant to be curated by the most avid users of the site. I don't believe the privilege list of Area 51 is even entirely accurate.