Dang, Robotech. I think you just wrote a lecture for Advanced Redline Fun. I was considering doing some tweaks to the 2008 Redline I recently acquired but now I think I'll just run some engine cleaner thru the ol' girl and leave well enough alone. At 100K on the clock I'm reluctant to do much mechanical.
You're going to hate me but the engine cleaners aren't going to do everything they advertise in your LNF Direct Injected turbo. Since the fuel is injected directly into the cylinder, it won't touch the intake tracks or back side of the intake valves where carbon buildup is notorious in a Direct Injected engine. Basically it will help with cleaning the direct injector nozzles and that's about it.
Honestly at that mileage the biggest things to look for are the water pump leak (if it hasn't been replaced already), timing chain, shocks, and the turbo. Some have reported major engine issues around that time too but the reports are few and far between...but they are there.
I would check your timing chains first and, if the guides/tensioners are worn, replace them and the chain. If the chains wore through the plastic part of the guides, got into the metal, and you're seeing metallic flakes in the oil, do an oil change, drive it for 500 miles, and do another to see if the oil is coming out clean.
If all that is good, some simple mods shouldn't be too hard on the engine. You can do intake if you like the noise, exhaust for either sound or looks (I like many of the aftermarket tips far better than the stock tips), and a tune. You'll be very happy with that setup, have a little more power, a little better (my opinion.. @skersfan
felt the intake made the bypass valve sound like a goat) sound, and a different look.
Beyond engine upgrades, most shocks go about 70K miles or so. If yours are feeling worn out (car bounces) or show signs of leaking, getting new shocks or upgrading to coil overs can be a performance upgrade too that won't hurt anything at that mileage. Anti-Sway bars, front brace, "backbone" brace and rear suspension brace upgrades can also be beneficial to handling and again, car mileage really isn't important here.
If you do a lot of hard driving in mountain roads, upgrade your brakes. At a minimum, go with better pads and, if it hasn't been done, drain and replace your brake fluid. Stainless steel lines also are helpful to the stock brakes. That will improve the stock brakes to a point where they should be far less susceptible to brake fade when pushed hard. You can go further with brake upgrades but unless you're REALLY pushing it hard for a LONG time (racetrack or hard driving on mountain roads for an extended period of time) a pad upgrade and braided lines should be more than enough to have a good, safe, brake system. Like the other suspension stuff, these kinds of upgrades are only going to make the car better with the mileage you have on it.