I can get 1990 kdx200 front forks for my kdx220 and I an pretty sure they will fit. Does anyone think this will make much of a difference if I get them on my 1997 kdx220?

The 220 and the 200 were the same bike, except for top end (including the carb). You may find some differences between the 1990 and the 1997 forks, but they shouldn't be deal-breakers.

why bother in other words

Nah. You can set up your current forks to work better than the stock 97's for a lot less hassle than changing the front ends.

IE: you'd still have to put a bunch of money in the 97's to make them worth a flip, and by then you could have just set up the ones you have now for a lot less time and money.

I wouldn't go back to 1990 KDX200 forks. You will need at least the 1990 brake caliper also. The axle is different also. The main thing is that the older forks are older technology, and won't work as well (assuming both are working as they should).

Oh wait, I totally read that wrong. You have a 1997 and are thinking about 1990 forks??? Absolutely NOT. The forks got a bit of an upgrade in 95, and those forks are going to be a better base to build from than the 1990's.