If you do go with a complete rebuild, this is what you SHOULD be gunning for... (using a 3" kit as an example)
1: FULL COIL SPRINGS. No need for poly spacers in the front when you get good offroad coils.
2: FULL 3" LEAF PACKS. AAL leaf packs are only as strong as their weakest point. Since XJ factory springs (non-UpCountry) are already soft, you want strong, load-bearing leaves to keep the arch up.
3: 3" hydro- or nitro- shocks. Bilstein, Rubicon Express, and OME are good selections.
4: longer bumpstops - front and rear. This will help keep the wear-and-tear down on your kit by limiting uptravel on both axles so that you don't bottom out when you flex.
Additional mods that will be useful in the immediate future...
4: BPE's - Bar Pin Eliminators - front and rear. Replacing shocks with the factory holes and bar pins is a royal PITA (wait until you snap a bolt trying to get one out... it's LOADS-O-FUN... :banghead
. These will make replacing shocks a breeze.
5: Bumpstop plates. These go great with extended bumpstops and/or stock bumpstops in the rear. The plates go on top of the rear axle and press against the bumpstop to limit uptravel on the rear axle. The nice thing about them is they're ADJUSTABLE. You just add/remove plates as you see fit.
6: Rear shackles. These are more for long-term goals. You won't need 'em right away, but in the near future you may see some settling of the leaf packs after a few hard trails and want to adjust your rear height more. These will replace your existing shackle and give you a definitive height based on the length of the shackle.
7: ACOS - Adjustable Coil-Over Spacers. Even more long term and pricey. These allow you to adjust the height of the front coils. Why do you want 'em? Wait until you get an offroad bumper and front winch (c'mon - you KNOW you want one!!!). The extra weight in the front will push the coils down plenty, dropping your ride height. The ACOS's will compensate for that rather than having to add poly spacers to get the same desired amount of lift.
Things to get if you encounter problems with driveline vibes after a lift.....
8: T-case drop. Start with this FIRST and FOREMOST. It's cheap, easy to do, and can under the right circumstances really help with vibes.
9: SYE - Slip Yoke Eliminator - Absolutely necessary for any kit over 3.5" lift. Gets rid of the slip yoke and shortens the driveshaft to improve your driveline angle to the axle.