besides the 100K maint stuff (most of it anyway*) I did front and rear sway links and bushings (amazing what some nice moog rear links will do for you on the cheap). I will do the front end this summer (Bilstein shocks bumped up an inch and replace everything that touches them). Oh, and I installed drilled and slotted rotors with Evolution pads. Probably $750 for all of that, maybe. Oh -- and led interior and BU lights.
performance I have $750 invested --- $150 in an airraid MIT tube (independent tests show the factory box with quality filter (I have a purolator pureone) flows just fine) and $600 Blackbear Autocal box / tunes. those two items have taken 2.9 seconds off my 0-60 times. The tuner gives me tons of flexibility for fuel choices and trans performance levels and Justin will do free reprograms with additional mods.
So for about $1,500 the truck is in excellent / mint mechanical condition and LOTS faster than it came from GM (gawd, I hate the factory tune).
the only other thing I will add when the money comes along is a Magnisun SC. I had SCs on my 3 Grand Prixs and really miss that kick in the ass when they wind up.
The best deal I got was the rear shocks --- they're the auto-level ones (forget the fancy name for them -- but not air) for $11.90 each off amazon. I was just looking up prices for stuff and grabbed those just because 2 new fancy OEM shocks set me back $24 total.
anyway
* plugs, wires, every coolant hose and new anti-freeze, front o2 sensors, belts, cleaned MAF and TB, flushed brake and PS systems, OEM trans fluid and filter and new pan with drain plug. etc