Torsion bars are the only drawback of the 98+ Rangers in my opinion. AKA Rides like A** lol.
As Adam said, they will sag over time, but that's nothing that can't be fixed with another set of torsion bars or a simple twist of the adjustment screw.
On your 08, if you want a pretty cheap "lift" you can find some torsion keys out of an 07 and lower truck and put them in place of your keys. It will pick up the front about ~1-2".