I have one and find that it suites my needs well as something to enter midi data and serve as an 88 weighted key synth. Some of the sounds hold up well when used to sweeten the mix..... on their own they are not up to the current standard. I would go to e-bay and see what people have been paying in recent auctions-- to find out what they were worth.
The new 8.2 goes for about $1000 street - the 8.0 is just as good - same sounds. $400 might be a bit low, but I'm sure you can get it for less than 6 bills. The feel is great, and if you can find the Vintage Keys or Vintage Synths expansion cards, they rock!
Daf (owns an 8.1, played an 8.0 at church for 5 years)