I didn't notice a difference on my '87 yj.I didn't have to much choice at time because I bought jeep with the emmisions stuff gone or unhooked,so I took easy way out.Go to http://www.shortwheelbase.com for some great info.
I did this to my cj (similar) but when i did it i removed the stock ignition and upgraded to MSD ign. I also put a weber carb on which simplified the process. I noticed a huge increase in performance, but I got rid of stock parts. I am a certified auto electrician (who cares) so if your not sure dont do it, my friend tried it and his jeep wouldnt turn off.
I did that to my '85 and had much improvement. No performance increase. No fuel mileage increase. It runs better from cold to warm, no more stalling at stoplights during warmup. It will even idle when warm. Hot restarts are easier. Still a worn out old engine but I was happy with the results.
Someone else on this board once posted that the results from the nutter bypass will depend on how worn out the parts-n-pieces are on your Jeep. You can spend the time to repair/replace all of that or not.