Coil spacers and body lifts add the needed clearance for larger tires, which gives you better ground clearance and depending on the tires you choose, better traction off road. Neither one affects the ride very much from stock because you're still using the factory springs.
I personally wouldn't recomend putting spacers much taller than 1.5" up front without doing something to lower the front diff, otherwise the cv shafts can get stressed out from trying to operate at extreme angles. Plus, because of the lever-fulcrum effect of the front independent suspension, 1.5" spacers provide roughly 2-1/4" of lift up front.(when you add the spacers, this pushes the springs down 1.5", but the springs are only a little more than 1/2 way between the arm's pivot and the knuckle end where the tire is mounted, therefore the tire gets pushed down further than the spring). I have offroaded quite a bit with spacers and they work great. My silver Tracker in my avatar pic was running a 2" body lift and 1-1/2" spacers, with 31" swampers, and it worked very well off road. My current trail rig, the Green Goblin, is running a 4" body lift, 1-1/2" front spacers with OME Struts, 2" Calmini rear springs and '91 Crown Vic shocks. A little trimming and it fits 33" Swampers very nicely. I took the swaybar off both trucks and never missed it. They both ride just fine on the road, too.
Wildgoody on here was making spacers after I quit. His provided a little more rear lift than mine since he went with 2" rear spacers(I think), so the lift was more even...
The budget lifts are well worthwhile, just make sure if you tackle your own body lift that the body is well supported and use thick wall steel and whatever you do, don't weld the body lift blocks top and bottom... Ask me how I know this...

(previous owner, not me...)