Interesting tie-in, Jeff.

The Theme Review team are actually in the process - even today - of improving the WPORG Theme Repository uploader validation script. Everyone benefits from automating the process as much as possible!

Also, regarding tools - several are available, and are linked from the Theme Review Codex page. The two most beneficial tools are both WordPress plugins: Debogger and Log Deprecated Notices. Next, of course, is the W3 HTML/CSS validators. The easiest to use is Unicorn, which combines HTML and CSS validation into a single tool. Also, the entire Theme Review Codex page is thoroughly cross-referenced to the Codex pages for the various required functions, tags, and hooks.

Everything we've been able to think of is there - but of course, if Theme developers have more ideas for how we can better communicate the quality guidelines, or help educate how to implement the guideline requirements (and why various criteria are required vs. recommended vs. optional), we're always open to such ideas!