I'm a little hesitant to offer advice, because I'm barely knowledgeable about building Jeeps. But I've found many times in life that it works best to improve my own knowledge and skill until my skills are no longer the limiting factor in performance. When the tools (i.e. the Jeep) become the limiting factor, THEN it is time to upgrade.An aired down stock TJ with an experienced driver is much more capable than many think.
When I was auto-crossing my Rx8, I followed this path, and never ended up modding the car - because it was always more capable on the track than I was. It was painful to admit, over and over ... but my skills were always the limiting factor. On the upside, I saved a lot of money with that in mind In this case, my goal was to become a better driver, not to win best time of the day. If my goal had been to win the day, then maybe I could have spent my way to a few wins.
I'll also second the advice to buy quality, depending on your goals. I plan to drive this LJ for a long time (been driving my TJ for 21 years). Whenever I did anything to the TJ, I did it right. Never regretted it. Well, there was that cheap-ass radio I put in. Been regretting that.
Of course, if your goal is to build, then go ahead and BUILD! It all depends on your goals.