I know several people who have ex-govt. Crown Vics. Great car far as I can tell. The ones I've driven are, like you say, reasonably fast, solid, handle and ride well. A mechanic I know has one with 300k on the clock, and all it's ever needed was fluid and filter changes, tires, and brakes. I bought one myself back in 2005 (low miles, light front body damage) but somebody snagged it out of our storage lot before I picked it up.
If you do buy en ex-cop-car, try to get one that's never been hit hard, or had suspension damage...both pretty common on police cars down here.