I could get almost 4" of additional rise (measured top of tire to wheelwell) in the rear doing the level sensor trick on my '98 LeSabre, but I stopped at about 2". I looked under the '04 and it looks like it would adjust the same exact way.
It does look cooler, but I did it mainly so I wouldn't bottom out so much on the poorly designed driveways everyone has around here on their postage-stamp-sized lots.
I don't know whether it really "stiffens" the rear on a launch any...some say it does, but I'm not convinced. I don't see how it would shift the weight ratio...maybe if you filled the bags with helium
2004 Buick Lesabre Limited, Gran Touring; Bone Stock
1998 Buick Lesabre Limited, Gran Touring; Mods: Poly sway bushings/endlinks, Tru-Cool trans cooler, Thrasher shift kit (med), PLIM, front PEM; Mods in progress: Alot of stuff, but slowly...