Drive both and see what you like. Personally I'd wait for the '05, but I still love my '01 and plan on keeping it for quite some time.

Mileage will probably be similar (translation: shitty).

Another option: I know they have quality problems, look , and only come w/ a slushbox, but if you really want an SUV but need good mileage you could check out a Diesel KJ. I like Xterras a lot better, but the diesel KJ should get a lot better mileage and still give you similar capabilities and performance (compared to the '04 - an '05 X will seriously outperform the KJ). I would mention a hybrid escape also, but they are just lifted cars.