Regarding the tag wiki system that was recently implemented on SO. I think requiring 100 upvotes in one particular tag to contribute to these pages is too high.
Firstly, trust the populace! I don't have to provide credentials to edit some detail about the decliene of the Byzantine empire on wikipedia. If the page is intended to be a wiki then it should behave like one. Anyone, even users who are new to the site, should feel welcome and trusted to read these pages and contribute.
Secondly, the success of wikipedia and wikis in general, derives from the fact that expert knowledge about a given topic provides a very small percent of the work necessary to make an informative page about that topic. The success of the tag wiki system is dependent on a veritable army of people who are relentlessly fixing grammar, reviewing the text for clarity, re-organizing content and providing depth to the pages by linking to them as many relevant SO questions as possible. In fact, the people who are the most qualified and probably the most motivated to make these changes are the non-experts who come to those pages to learn from them.
(A similar request - now status complete)
There seems to be a misunderstanding. According to the meta thread I linked, the requirement for editing the tag-wiki page is "if you have more than 100 upvotes on non-wiki answers with that tag you are entitled to edit the wiki section." This is very different from 100 rep.
I agree with both @Robert Harvey and @Tim Post. Feature request: make the reputation requirements for tag-wiki the same as community wiki - 100 rep not 100 upvotes (from non CW answers in a particular tag).