I have an '03 with 118+K on it and aside from regular oil changes didn't exactly follow the recommended maintenance schedule over the past 7.5 years.
Over the past couple of weeks, I decided to service a bunch of "ride-specific" items all at once so that the parts could all start working together at the same time and benefit from being set up correctly as a unit.
Specifically, I had installed new KYB Monomax Shocks (yes, I was on the originals up to 118K), new (upgraded) brakes and rotors, new tie rod ends, new Sumitomo A/T tires, my 1st alignment and FINALLY bought and installed the EE Rear Sway Bar upgrade that so many on here have raved about.
Well, suffice it to say that not only does the truck "feel" better, it now rides better than ANY truck I've ever been in. Yes, it still obvious that I'm driving a pickup truck, but now I can actually feel and sense the road in the seat and through the wheel much like a European Sedan and it's an amazing combination. It's become extremely fun to drive.
If your ST is paid off or close to being paid off, don't be scared to put some money into it. All of the stuff I had done above cost closer to $1500.00 than $2000.00. If your mechanic will let you, buy your own parts and have him install them. You'll save quite a bit.
Bottom line is, these trucks are generally well built and forgiving so don't let the 100K milestone freak you out. My ST is now actually WAY BETTER than the day I drove it home new back in 2003 and I love it.
EDIT: The raves about the EE Rear Sway Bar are dead on. It's utterly amazing how much more grip there is in the rear end and also how much more stable the truck is with the reduced body roll. My only regret is not putting it on sooner.
