Resale will depend on the two tractors your comparing but most of the wide gauge row crop track tractors have very good resale value.  Replacement tracks will cost more than tires for an MFD and will need to be replaced a little more often but we're talking about a dollar an operating hour difference so if the track machine gets a little more done per hour it will come out ahead dollar wise.  Maintance on the track undercarriage should be minimal on most newer machines but like an MFD if you let a hub leak the oil out it can get expensive but not as bad as an MFD. 

One of our neighbors just bought a pretty clean Cat 55 with 5,500 hours on 80% 25" belts (90" centers) for somewhere in the lower 30s and it would be pretty tough to buy a comparable age and hour MFD for the same money, I'm not for sure what year it is but it has the two piece boggie wheels and the updated fuel tank so I think it's at least a late '97 or '98 machine.