Upper intake is important, but IMO, even more important is how old the lower intake gaskets are. I replaced mine at 77K and they were wasted. I also replaced the Upper Intake with a new Delphi unit, but the original was still fine.
How many miles are on the one you're looking at?
My 99 has been VERY reliable and keeps on running strong! I'm at 100K and have only done the typical things...brakes, rotors, a tune up. The upper intake and lowers were the biggest job I did to it. I also had to have the heater core replaced. It'* not common for them to go out on a H-body, but still run the heat and try to detect an anti-freeze smell.
Check the transmission for shift-smoothness. Also smell the transmission fluid and try to detect a burnt smell.
Get as much previous-owner information as you can on the car. Previous owner maintenance is a strong indicator of what you'll be in for.