They're really a pretty troublefree design. They wouldn't have lasted 200K if they weren't! (Think about this... at 3000 rpm, each injector fires 100 times a second... in an hour they've fired 36000 times..... in 200,000 miles it probably comes out to about 360,000,000 cycles!)
It's a low-wear part. It's possible for there to be some deposits on them or a tiny bit of crud blocking some flow. They aren't really likely to wear out but they could need a cleaning. There are lots of other things I'd spend money on first to make sure the car runs perfectly.
One of the main things is vacuum leaks, and the injectors can come into play here because there's a rubber seal around each one- it can leak and cause mixture changes by introducing excess air into the intake.
New seals are $3 each. It also wouldn't hurt, and will help if there's any deposits, to run a bottle of Techron fuel system cleaner through the system. That's about $12 per bottle.
I think that's about all you need.
--
Rob Bareiss, New London CT ::: '86 244DL- 215K, 87 244DL- 230K, 88 744GLE- 198K, 91 244 180K