[V8] Poor fuel economy

[gbmarc at cox.net]

I realize that when I come to sell my car I will have to post with a pseudonym as everyone will know what a horrendous catalogue of complaints my 200K mile car has!  Anyway . . .
I'm currently only getting about 14mpg around town and 17mpg on a longer run. The computer reads about 1 mpg better but I know it's lying from filling up and checking odometer readings.
The car also has an uneven vibration that is noticeable when stationary at idle. The Oxygen sensor is about a year old and the plugs are even newer. The car seems to accelerate OK, but then again, I doubt I would notice the difference between 190bhp and 245bhp if it happened slowly over time.
Any obvious quick checks I can make?

Mark.