We used to have a 4430 with 35000 hours on it and the only thing we had done was split it once and do the powershift. It wore through 2 front end loaders. When we sold it, the guy jumped in, turned the key and drove it home.
Now we have a second hand 4240 that we did a motor on at around 12000 hours (we got it with around 10,500). We put very few hours on a tractor anymore, and with a new circulating heater it doesn't need ether to start, so it should last a long time.
I am not sure the new ones are that much of an improvement, although the comfort is nice, and the seat for kids would be pretty good (They are $700 at the dealer in town).