Actually from what I hear the 97-01 are the most cost efficient of the Q45's to own. But the engine set up wasn't the best, A knock sensor for each cylinder cmon now. And the coil packs weren't nearly as good as the G50's.
The downside like i somewhat mentioned are the price of mataince and parts are high but you can get them from joe who has OEM parts at the cheapest that I know of
http://www.infinitipartsusa.com Do the easy work your self then you will have a great car at a OK price.
If its in good shape go for it.
Welcome to NICO.