I wouldn't go to that big of a extreme in saying WAY underpowered, 3hp gain isn't that much. Dixie Chopper sets their units up to run at 3650 RPM's with the deck engauged to assure you are getting the full 20hp from the engine while mowing. Most other OEM's set RPM at no load so by the time you engauge the deck you have dropped below the RPM range for max hp.
The owner and founder of Dixie Chopper Corp. doesn't believe in building under powered units, If it doesn't pass his own power test he will not put the unit on the market.
With that said, It's my opinion you should have no problem with this unit.
As for it's worth, It depends on how well it's been taken care of and maintance standards. I've seen 1yr. old units I wouldn't give 500.00 for, (Rode hard and put up wet).
South Florida, You may want to check your RPM's and tweak it up a little. It just mite help your bogging problem a bit.