Hobie has made some nice improvements to the Mirage Drive throughout the years. Even if you have an older model, you can take advantage of some of these. Here's three that I recommend:
1. The new pedal adjustment assembly works flawlwssly on the old drives. I've had these for over a year now and wouldn't go back to either style of the old pins. They are illustrated in the picture below.
2. The new drivewell seal fits the old Drives as well as the current models. I've been using a rudamentary form of this for years and am a big fan. You'll notice one in the pictures (on the right).
3. ST or ST Turbofins work just as well (maybe better) on the old drives as the new. Either will give you a nice performance gain. I use Turbos; my wife prefers the STs.
4. Pedal adjustment decals -- I haven't actually tried these yet, so I can't "recommend" them; but I'm almost sure they will work. It's a lot easier to use the numbered index than counting holes when adjusting the pedals for different users or boats.
All the parts can be found in the new catalog.