I have done many of the things that people are listing here. Many of them I don't really regret though. They were necessary steps to get me to where I am, with the money I had at the time.
I locked my d35, but that only cost me 50 bucks, after I sold the locker.
I started with AAL in the rear and they did sag, but that only cost me 25 bucks more than starting with the full packs, and they lasted me 6 months of wheeling, so that was worth it to me.
Also, I started with just a 3" lift, that worked pretty well, but didn't work near as well as my current 5" setup, but was much cheaper, and a good base for me to build upon.
The only mod I really REGRET is not spending the extra $200 bucks to go to 4.88's when I installed the 8.8. Instead I stuck with the 4.10's in the 8.8 and geared the front to match. Works ok with my current 32's, but I am in need of upping my tire size, and these gears are really going to suck with my next set of tires (currently run bias Swampers and will more than likely go with these again).
So, it is all a learning experience, and I wouldn't have near the wrenching and hands on experience that I have, let alone wheeling experience, if I had just saved my money and done it "right" from the beginning.
The biggest regret I have when it comes to my Jeep, is not caring a little more about it a couple years ago, and spearing it some body damage. At that time, it was just an $800 rig, so I was like "who cares?" Well, now I have a lot more than that in it, and I care enough that I want it to still be functional for a little while longer. If I had only spent some of the first money on body protection, then it would be in a lot better shape than it is today.
HTH someone