There is some very good information about different lift options here: http://www.4x4wire.com/toyota/4Runner/tech/suspension/

a review about the spacers found here: http://www.4x4wire.com/toyota/4Runner/tech/suspension/phil.htm
"On-road this setup is pretty good but it has stiffened up the truck a bit too much. You do feel the bumps. Off-road the added height helps along with the 33" tires. Articulation is very limited. Stiffness and lack of articulation is due to the spacer/spring combo, too much preload of the progressive rate springs."

He fit 285/75/R16 with the 1.5" spacers. it is definitely the cheapest way to go.