Q:

Limit tag selection based on minimum rep? 

About 90% of the edits I do on SO are re-tagging poorly tagged questions, and the vast majority are from people posting their first question.  It's common for them to take the nouns from their summary or first line of the question, and just stick that in the tags field, which means there's generally no mention at all of the stuff that should be in there. 
My suggestion would be that low-rep users cannot make a new tag, i.e. they have to pick one from the list of existing tags.  A stronger form of this would be to limit them to tags which have been used at least, say, 10 times before, although that's more dubious. 
This would, I think, improve things considerably regarding these "wildcard" posts. 
Thoughts? 

A:

From the SO faq:

What is reputation? 
...
Amass enough reputation points and Stack Overflow will allow you to go beyond simply asking and answering questions:
...
250    Vote to close or reopen your questions, create new tags

So they should be getting an error message if they're entering completely new tags. 
What's likely to be happening then is that they are choosing inappropriate tags and, other than introducing complex parsing of the question, I don't think there's a lot that can be done about that. 

A:

We already require 250 rep to create a new tag. 
Unfortunately, users with 250+ rep tend to be nearly as bad.  They'll create the tag, but even if someone deletes it from that question the tag still shows up as available for a long time.  So tags like 'visual' and 'server' just will.  not.  die. 
I think we really need two other things:

The ability to ban the use of certain common bad tags (in a public place where users can see which tags are banned). 
Warn users when they pick an uncommon tag (used <10 times).   Let them click through the warning, but at least give them some immediate feedback that they might be doing something wrong.