I do not know what its worth but I have a 19hp/44'' Toro Z master and it bogs down in thick grass. I also mulch too, but I wish I could have gotten a bigger engine. I would at least find a 50 inch Dixie with no less than 23hp 25 and 27 is where you wan't to be.
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.
Id say price wise below $5000 it dosnet have alot of hours and dixies hold ther value well casue of thier toughness. The rule of thumb and this comes from one of the smartest people I know when it comes to mowers. Is 1/2 HP for each inch of deck. And the LT200050D like you are talking about has a kohler on it. kohler dosnet really give you the turth on ther HP ratings. Its probably around 17 if you put it on a dyno. Where as the generiacs they use are right on what they are listed at. But if its under $5,000 id say its worth it. ( and in good shape) dont look at dirt, look at belts, pullies/spendals. And dents. Dirt washes off. And the stainless steal from dixie has a lifetime warantie aginst rust.