Pretty sure my forks with 21,000 miles have the same oil and seals. Last time I rode they felt very spongy, but didn't bottom out. So I decided to add this to my winter maintenance list. (1) should I replace the seals even if they're not leaking? (2) Do I need all parts: 7, 8 and 9, 17, and 23 on page below?

https://www.bikebandit.com/oem-parts/2007-suzuki-gs500f/o/m16095?a=2#sch649430

I wouldn't replace the seals if they're not leaking, best not to disturb nicely bedded-in seals, -they're probably better than new replacements would be (aftermarket ones can be less than top quality).
But I would replace the fork oil.

Agree with leaving the seals alone if they're not leaking. I've had fork seals last over 50K miles on some bikes.

It's a good idea to carefully inspect the leading edge of the tubes, you'll likely find some very small pits or dings. It's those nicks and dings that tear up the sealing edges and cause the seals to leak. Get some extra fine steel wool and lightly buff the tubes.

Changing the oil will help some. The fork springs are still going to be very soft though.

Thanks for the tip, will buff them. I know the stock springs are soft, but Im 150lbs and have ridden on them for 2 years now. Tough to justify $100 replacements at this point.

Don't change the seals if not necessary. Try 15 weight fork oil rather than ten - stiffens em up a bit with very little hassle. The measurement for how much oil for my bike was 110mm from the top of the fork to the oil level or 380 cc.  If you do need to split the forks you have to use an impact driver to get the bottom Allen key off. The book says to try a broom handle to stop the other side of the bolt from spinning but that has never worked for me. 

I did a little write up, in case it may be of use for you.

http://gstwins.com/gsboard/index.php?topic=70830.msg851128#msg851128

The broom stick did come in really handy for the 2004+ shocks.