Are there any decent performance upgrades available? Are the "Chips" out there any good?

To get any significant improvements in performance you will have to spend far more $ than the value of the vehicle. The main issue is power to weight ratio. You have a modestly powered V6 in a vehicle that weighs 4100lbs. The only upgrade that's going to make a big difference is turbo charging and then you're spending $8-10K on a car worth $3k.

Are you 2wd or 4wd? Unfortunately there are no chips, or drop-in/bolt-on upgrades available.

Reduce weight. Delete the spare tire. Pull out carpet. Remove the rear seats. Remove running boards, roof racks, etc. That will make it faster without adding power.

Swap in a more mod friendly engine and a manual transmission, and start spending some real cash.

Swap in a vh45 or vh45de and make 278 - 310 horsepower respectively and keep reliability and fuel economy. VH45DE's are hard to come by.

Addi an intake and exhaust. This will make it louder and add a tiny amount of power at WOT, but it isn't worth the droning you will hear on the freeway.

Turbocharging has been done on R50s, but it isn't really viable as it is prohibitively expensive and ruins your reliability completely.

Regear your rear differential to get more power at the wheels and sacrifice RPMs at high speed as well as reduce your top speed.

I have a 2004 as well and have looked into this many times. If my Pathfinder lives long enough, I will swap a VH45 into it. They really didn't give these things enough power.