Probably for another threads discussion, but real suspension lifts like the 4" superlift has a lot more benefit than just 1/2" more at normal ride height than an OME + spacer 3.5" setup.

To keep this short, sweet and to the point... imagine suspending the vehicle in the air so that all of the tires are hanging at full drop. With a 3.5" spacer type setup, the distance from fender to hub is only as much as the stock control arms, tie rods and CVs will allow. This may be only 1-2" further than where the hub sits at your normal ride height (so say 3.5"+2"... you're looking at the wheel dropping a total of 5.5" from the position of a stock jeep). Now, a 4" suspension lift retains all stock geometry... so from the start you're already 4" further down than the position of the hub for a stock jeep. Add in the suspension travel of 5.5", and you're looking at a hub position change of 9.5" beyond a stock jeep.

In terms of clearance, this means that the belly of your jeep will keep tire contact for 4" higher belly clearance than a spacer lifted jeep would.

If you're just cruising around the streets, yeah there's really not much difference other than increased wear & tear due to the angles of 3.5" VS. OEM angles with the 4" suspension lift.