Are you sure you really want to sell the HV unit?
I use Comfort and HV together - they complement each other really well. For my uses, I found Comfort lacking in a few major areas (just no-where near as flexible and powerful as HV for the more pure HA functions). I also found Comfort to be more cumbersome to program.
Sayting that - I know a few people who do everything in Comfort - but I wouldn't want to!
Re value - have you had a search on the HV yahoo group - I know there have been a few up for sale over the last several months. Mostly US based though.
Cheers,
Paul.