Here's an amazing technical thread about the benefits of throttle body spacers & boring out throttle bodies, with real documented tests. Tons of good info, get ready to read!
http://www.rockymountainextreme.com/showthread.php?t=30793
Technically speaking, that thread just has more supposition and theoretical rambling about
spacers, as none were tested.
I want to say that JP Mag tested spacers, with zero improvement in anything.
Bored throttle bodies I could see (more volume usually helps power), but spacers should have some kind of "runner-lenghtening" effect, if any, and 1. they're pretty short and 2. Jeeps do not often run flat out at the RPM's that longer intake runners would help.
But this is America! Throttle body spacers are pretty anodized colors, and it's not my money. Have at it, and long live capitalism!!!