Before you go getting psyched about a bike that is 500cc+ check the insurance rates. More than a few companies will jack up your rates if you've had a gap in insurance. Some companies have a policy that if you've had a gap of 5yrs or more they treat you as a new rider regardless of how long you've had your license. If that is the case, you'll still pay through the nose even if you're going on 26yrs old.
Nothing wrong with getting back out on a smaller bike for a season or two. There is a world of difference between the Ninja 250 you had and a modern 300cc. If I were riding in the city with some trips out to the country I'd give a serious look at the CB300F or R. The upright ergos would be much more comfortable in traffic and for soaking up potholes. If the difference between a 300cc and a 400cc for insurance isn't too bad, consider the new Z400 (if your budget allows). Again, the more upright ergos are so much more comfortable and you still get the same kind of handling out of it. Plus, no expensive plastics if you tip over and less attention from Johnny-Law because you don't look like a little racer boy.