When I was researching lifts I was looking for that information as well. Here are the things I found that I had to think about. Hopefully it will help you.
In my mind, the answer really becomes a spectrum of possibilities and all answers probably should start with these words instead: “It depends”.
It depends on what lift you choose. If you go with a kit what parts are included? If your lift is exactly what you said (new springs, shocks, and tires) no less and no more, then the answer will probably be way different than if you buy a high-dollar comprehensive kit from a major manufacturer.
It depends on what your predisposition for things that are “not exactly right” or “not the absolute best” or “not the closest to factory geometries”. You will need to figure out for each component or possible component, if you will be satisfied with a given choice.
For example – will you be happy with a front axle that shifted driver-side? If your kit does not come with a track bar fix (new bar, new bracket), or if you don’t fix it yourself (drilling new holes in the axle-side bracket) it will be. How much depends on the lift.Is that an acceptable thing for you? If dollars are your main concern than you might possibly get by without a fix for this “problem”.
U-bolts. It depends on how okay you are with running used u-bolts. If you do even rudimentary google-sleuthing you will find answers on both sides of the fence from “not a problem” and “why worry”, to “you are brain dead if you don’t replace them given the low dollar cost”.
Brake lines. This one comes with an extra factor – safety. How willing are you to risk failure of the old lines should you choose to re-use them? During some four-wheeling maneuvers, you may stretch the old ones to the failure point. Think about both front and back. But not all kits come with them.
Shackle angle changes in the back. This one is primarily a ride-quality factor. Do you “need” to fix it? Not necessarily, but you would gain better ride and probably extended life out of your parts if you did.
SYE kit or transfer case drop-down. This one cannot be known ahead of time whether or not you will need it. But if you need it, you need it, so you ‘need’ to be prepared to spend several more hundo, unless you like changing u-joints.
Steering dampener – you may or may not think about replacing this during a lift install. But if you want to have a fresh start maybe you do need it.
Other bushings and hardware. How about sway bar bushings or sway bar link bushings, or the sway bar links themselves? Needed? Maybe, maybe not. How fresh do you want to be? How many $ do you have to spend?
Broken pieces – if you break things during the tear-out process, you “need’ to be ready to buy new parts. Shock mounts come to mind.
Bump stops – as already mentioned – for less than 20-30 bucks you can get new ones. If yours are in good shape then maybe you don’t need new ones, but even then you at least you need to be prepared to find a way to extend them (the puck thing some people do). Could you drive your rig on a three inch lift without doing something about them? Probably, but you would also be inviting broken parts.
LCAs - Some people will say you should look at new LCAs at 3 inches. I had one guy say I should go long arm at 3 inches. Some kits have them, some don't. Do you really need them? Not really sure, but you do need to know what the trade-off is.
