Ram 2500 - which towing features are best/good/unnecessary?

I would agree that since you're buying used and already looking for needle in a haystack, the 2500/3500 distinction on a newer Ram is moot. Functionally there's almost no difference and the almost can be eliminated for under $200.

Compare what you're seeing used to what you can get new at one of the high volume Ram dealers like Dennis Dillon. Go easy on the trim level and you might find that new doesn't make for much of a premium over what you can find on the used market.