Renewal will be about $65 and your domain is low $xx unless you develop it. I would keep it, not sell it
The domain is a registered trademark in several classes. Without permission from the TM holder, you risk losing it if you use it for anything related to their business i.e. they could take the domain without paying you a penny and/or they could sue you for damages.
Because twitter can't put a pattent on microblogging. And I wouldn't do a url shortening site because they don't make any money, half the time people use scripts that automatically shorten their urls from the site so they don't even end up ever visiting. And when they do visit, they are the for one thing. To make their URL shorter. That's it.
.IM will never be popular, most people don't even know where the Isle of Man is, .IM is the same as .WS, .TV a waste of money.