4 inches with block and spacers is WAY too much. Not only will it look incredibly stupid, it will be very dangerous. That method can give you max 2" of lift if you really want to be cheap. Stay away from lift blocks unless it's a strictly street ride. My suggestion: save up some extra $$$ and do the lift right the first time. You will get a much better and safer ride. Also, unless you have experience with any of this, don't go over 2.5" to 3" on your Cherokee because you will need quite a few extra modifications for it to work and drive well (driveline vibration, steering component stress, etc..).
I'm going to lift my Cherokee 3" when I save up some money. I'm getting a Zone lift kit - http://zoneoffroad.com/product?ki=34&vi=959 . It's a high quality starter lift kit. Always beware of "budget boosts" and avoid Rough Country budget kits.
Good luck!