If my experience is typical then you should definitely go for it.
After dreaming of owning a 911 since I was a little lad I finally bought one in January this year - a 2000 C2 manual, 55,000 miles, FPSH etc. So far, it's been everything I expected and more. It's used as a daily driver... covering short journeys to the office or longer trips to see customers and every time I get behind the wheel it puts a smile on my face.
Only problem I've had so far is a failed MAF sensor, which caused it to run rough at low revs, but the place I bought it from replaced it under warrantee and other than that it's been faultless. It returns high 20's on a run (but I've seen 30+ on the odd occassion I keep it to 75 or so) and low 20's knocking around.
Just put 4 new Tyres on it, and they're not too bad... 265/35/18's on the back and 225/40/18's on the front, correct N rating, £640 fitted.
But at the end of the day you don't buy a 911 for the MPG or because the tyres are reasonable, you buy it for the driving experience. It just feels so different to anything else I've ever driven, partly because of the engine at the back, but mostly becasue the major controls are just wonderful, particularly the steering. OH, and even with a standard exhaust, it sounds fantastic between 4 and 7K.
Buy the right car at the right price and you'll love it.