In general, I tend to have a much lower bar for the amount of improvement to approve or implement edits in the title. This is because question titles appear in many more places than just the question itself:
- The front page
- On-site search results
- Related and Linked sidebars on other questions on this site
- Hot Network Questions on this site and others in the Stack Exchange Networks.
Having well-groomed titles is important. Fixes like LaTeX improvements, bad grammar, picky grammar issues (e.g. 'How to X' → 'How do I X'), spelling, and so on are definitely worthwhile. Larger fixes (like making the question title accurately describe the actual question in sufficient detail) are a must.
That said, having title case is... pretty much not a problem for me. Things like
What is the Physical Meaning of Commutators in Quantum Mechanics?
read just fine and don't jolt the reader too much into a 'hmm, what's with the language there?' note (I tend to find). I don't fix such titles and would tend to reject as Too Minor if that is really the only possible improvement on the post.
On the other hand, a quick perusal of the current front page indicates that the questions whose titles lend themselves to the use of title case (currently the only one being A Confusion in Rotational Dynamics) have the sorts of titles which are not particularly descriptive of the question. Longer, full-sentence titles which actually ask a question will tend to look weirder in title case than short statements about what area the question is generally in. In such cases, the question is better off getting a completely new title which actually describes what is being asked.