Dudes, the I forum is a little slow, probably should have tried the main 5th gen forum for more responses. In addition, I've found that the members of this forum usually chime in when help is needed, but are less inclined to provide purchase advice as it's ultimately the buyers decision.
+1, on the fact that the I35 is a great car. An '04 with that few miles is probably worth between $5K -$6K as per KBB, but probably not worth that on the street depending on where you live. If it were me, I'd pay around $5K for something that sweet with low miles, but only because I'm an enthusiast and love these cars.
I have an '02 GLE with 107K on the clock, and it runs well. I've done a fair amount of work (tires, brakes, all suspension, cvs, entire exhaust, radiator, plugs, coils, gaskets, water pipes, and entertainment system), but only due to age and preference, not failure. I've actually only had two parts fail on me, and that was the Radiator and muffler. The transmissions in these cars are bullet proof if you take care of them and change the fluid religiously. I change mine every 12 months, but that's just me; the manual recommends 24 months I think.
Ultimately, if you decide to buy, I think you'll be pleased. You should however be prepared for the fact that you are still dealing with a 13 year old car that may need work due to age. Just remember, that if things do go wrong, the forum is here to help. We do it for the love of the game!