Sounds like a reasonable deal to me.........$67xx is a little high, butthe car has low miles. I'd buy it. If you haven't finalized the deal, check out
http://www.edmunds.com/used/1998/pon...um1.1.pontiac* Maybe you can use the info as leverage to save a few more dollars. Good luck!
I've never tried, or heard of, those plugs. The iridiums are pretty tough to beat.
Unfortunately, there's not a lot of good info out there about modding GTs. It's too bad too, the 3.8 is a great engine even without a blower. ClubGP is your best bet. Also, check to see if you have a local chapter of ClubGP........you will learn a ton about your car from other members.
You can buy a lot of performance stuff for your car used on ClubGP. You'll save a ton of money. If I were trying to get more HP out of a GT, I'd start with a CAI of FWI. Then I'd add a DHP or Intense performance PCM. Replace your stock thermostat with a 180* stat. Replace the u-bend in the exhaust......or better yet, get a cat back system. The cat backs are expensive though. Throttle body spacers keep your TB cooler which will help out. Headers would be nice but are expensive as hell. Roller rockers are helpful as well.
Hope this helps. Congratulations!!