I say, keep using it the way you have been as long as it's getting the dishes clean.  There are plenty of KitchenAid dishwashers out there that are older than yours and still going strong.

I don't know for sure, but the electronic controls on the series 23 Superba Selectras may be the "new and improved" Whirlpool version which is far more reliable than the failure-prone Hobart type on earlier Selectras.

If there are any weak links in the mechanics, they're probably the wash arm support and the check valve.  If the wash arm spins freely, it's still good.  If it scrapes or chatters its way around, you'll probably need a new support.  Looks like you may have some calcium or detergent residue that has built up over time, which could keep the arm from spinning freely.  The wash arm lifts straight up and off.  You may want to remove it and see what it looks like under there.  Just be sure when you lift it off, all four tips of the arm are in the clear from the lower rack's guides on either side of the tub.

The check valve is a little rubber flapper that opens and closes depending on the function, like washing vs. draining.  They can get stuck open which often causes an "urping" sound that can be heard through the air gap (the thing on top of the sink to one side of the faucet) or the sink drain during washing and rinsing.  A stuck check valve can diminish the amount of water that's delivered to the upper wash arm.  There's a GE part that works as a replacement.  If you do a search here you can probably find the part number.  It's an easy thing to change out if you're handy with a screwdriver and perhaps a pair of pliers.

You'll have to scrounge up most other parts for your machine from sources other than appliance parts houses, but they're out there.

You can get touch-up repair for the rusted plastisol areas on the racks.  You may have to do some looking to find it in blue, though.  I found Maytag brand (not that Maytag) in blue a few years ago at an appliance parts store that had a lot of old stock, but it was really blue compared to the blue shade of the racks.  Others here may know of a brand that matches better, but all I've ever found in hardware stores was gray or white.

You're wise to hang on to your Selectra.  It gets the job done faster and in many cases better than its modern day equivalents.  Plus, KitchenAids tend to have a timeless design that holds its own even in a brand new kitchen.  Their stand mixers are a perfect example.