That's basically my line of thinking on the issue too. But, the engine it uses was cancelled so I'm afraid parts will eventually become in short supply.
There's plenty of parts to go around, and in many cases, if you want performance-related aftermarket parts, there's plenty of those, too. If you have to do a bit of mountain road or hill climbing, the 2JZ motor has great torque from 3000-4500 rpm. I only wish the roads here allowed me to use that part of the sweet spot...
The interior trim is always top-notch; however, I've noticed that people who wear lots of jewlery tend to scratch the metalic-painted or black plastic trim after a few years. But the seats are firm, bolster you in all the right places, I never seen one that was ripped at the seams or torn from normal use. The steering is damn near inch-perfect (why the competing 3-series BMW took the way-too-light steering route is beyond my ken).
There's a few little issues with the car: 1) CD players seem to have less tolerance than other Lexuses. Some home-burnt disks are a wee too thick to fit in the loading slot, and it will jam the unit. Never use one with a label or decal pressed on it, it's guaranteed to cause a problem with the IS's CD player. 2) Clicking noises in the lower right of the dashboard. A/C servo mix (mode and temperature) motors tend to bind. They rarely cause actual performance A/C problems, though. 3) Oxygen and Air/Fuel sensors burn out quite frequently on every Lexus product, especially more recent cars. A used one is no exception. Any other major issues (clutch, tires, some interior trim) are wear issues that can be affected by the driver's habits.
The only downside of the IS to the rest of the cars in this comparison, is that the IS tends to go through tires; 15,000 miles is an average, but if you always keep the car aligned, the tire pressures right, and rotated on time, it's a small price to pay for it's best-in-this-group handling. However, 17" tires are getting less and less expensive (you might say 17s are the new 15s).
So what if the styling is dated? I prefer to own something that has a lot less flash. Beauty and flash is great for that other guy's car, I say.
To be on the safe side I'll get one with an extended warranty, if keeping it until 2014. Seven more years is a lot to ask on any used car (and driver), though.