Maybe the GitHub requirement[0] will raise the barrier to entry? I never used the old plugin site but I'll give the new one a chance. GitHub will make reviewing plugins so much easier.
[0]: https://github.com/jquery/plugins.jquery.com#how-it-works
[0]: https://github.com/jquery/plugins.jquery.com#how-it-works
Reading web mags like DailyJS and Smashing magazines are probably a vastly superior way to know about high quality jQuery plugins. These mags are like the academics journals, if your plugin gets published, there's a shallower limit to how terrible it can be.
I think it's more important for jQuery to provide a more flexible module/plugin system that jQuery itself is built on. Many people are actually asking for easier ways to have their own customized jQuery builds. There are ways you can do it now, but they are pretty involved. This is one area I'd definitely like to see jQuery improve on.
Any time developers want to be involved in a collaborative project, they generally have to conform to an agreed set of best practices. For jQuery plugins available through the plugins site, this now means using their GitHub-based system. If a developer's code is so tied to a particular set of tools that they can't make adapt to a new system, that's something they need to deal with, not the jQuery Foundation.