It appears that there is no ability to suggest edits to tag wikis on meta (at least, I can't). It also appears that several tags that have excerpts are not showing anything on the tags page (e.g., status-completed).
I wouldn't mess with meta tag wikis -- we plan to export all the common, standard meta tag wikis from meta.so.
(There might be an exception for topic specific, special per-site meta tags but these are quite rare in my experience.)
I definitely encourage anyone interested to assist in editing the main site tag wikis, however, particularly the page 1 tags.. please!
I just unlocked editing of tag wikis on all metas. My plan is to keep the "big" ones in sync provided they did not diverge.
If the community decides to put a community "spin" on any of the meta tag wikis, that is fine in my opinion.
Clearly you should (and can) edit any tag wikis for the blank tag wikis.