Title is a perfectly acceptable thing to add but it really isn't about disability accessibility. The WebAIM community has extensive discussion on this issue here (although that thread gets a little bit bogged down in arguments about opening in new windows). The short summation of the issue in most user agents, title is only accessible via mouseover tooltip: screenreaders only read title by default configuration in a very small number of cases, and keyboard-only users have no access to the attribute. Moreover, in most cases (all over dreamwidth, for example), people use "title" as a repeat of "alt". The only benefit this adds in user agents is to people who are doing mouseovers and want the tooltip; screenreaders will already be reading the identical alt text.

Jared Smith has a fabulous summary of when title should be used and for what purposes. A brief excerpt:

Title is great for conveying additional *advisory* information that
might be helpful to sighted users who do not use a keyboard or for the
few screen reader users that might hear it. It's great for providing
additional cues, instructions, or details that are useful, but not
vital.

...

My general recommendations:
- Use title if you want to when advisory information might be useful.
- Make sure the title text is brief and not the same as the visible
text or alt text.
- Recognize that many (most?) users will never know the title text is there.
- Do not use it for vital accessibility information, except on frames
and perhaps form elements that do not have labels