When replacing the brake pads and rotating the tires on our 2000 Grand Prix, the rust on the undercarriage was quite noticeable. Not really any worse than it has been on several other vehicles, but it bothered me.
Probably pretty normal for a car 8+ years old with 65,000 miles on it.
The car is probably good for 200,000 miles and we only drive it about 8,000 miles a year so it`s possible we might own it another 10 or 15 years.
The deciding factor for my changing vehicles is usually when:
1. I see something I think I have to have.
2. The vehicle we are driving starts showing rust.
Emphasis on #1.
#2 is automatic. Rust shows up, it`s fixed and the vehicle is gone.
In the 8+ years, I haven`t been interested in anything else so the GP could have an extended stay.

To the point:
Anyone have any ideas or experience with something to use to help reduce the rust on the undercarriage?
I spray it off with both the hose and a pressure washer regularly during the warmer months. During the winter, I periodically go through a drive-thru wash that does an underbody spray. Hopefully, that helps remove some of the road salt, but.....
There might be something I can spray on that would help. I`m not looking for something to dress it up for show. I want to stop as much of the corrosion as I can.