Do more tags mean a better question? a worse question? Is this even a relevant metric? I feel like more tags are indicative of an unfocused question or a question that is desperate for answers. Any data to support or refute this assertion?
I doubt it indicates a better/worse question, although it might indicate a newer user.
Before I understood how SE worked, I used to always use 5 tags because I thought it meant I would get more views. I'd actually spend extra time trying to figure out a 4th or 5th tag, even if one wasn't actually needed.
Now I understand how SE works better, and only use more tags if the question warrents more tags. And it turns out, most questions I ask don't need more than 2, maybe 3, tags.
It's not a relevant metric, quantitative metrics rarely are.
Empirically, questions that have five tags (the upper limit) tend to be better quality wise from questions that have a single or two tags, because the OP put a little bit more effort in categorizing the question. Four/five good tags is a hint that the OP is familiar with the site, but just a hint, the question itself may be crappy.
Then again, it's not extremely rare to see questions (good and bad) with three or four useless tags (think: meta tags). I don't remember seeing a question with five useless tags, let's hope the careercareer-developmentsoftware-developmentsoftware-engineeringbest-practices beast remains a mythical one.
We seem to have a bigger problem with tagging than other sites, at least the sites I frequent. If you take a look at stci, tags, tag-blacklist and tag-merge questions you'll get a better idea of the various tagging issues we've had (and in some cases continue to have). The first Structured Tag Cleanup starts tomorrow, hopefully we will get rid of some of the most troublesome tags.
Now, let's see how we can retag this question, because discussion alone doesn't say much...
Interesting SEDE queries