well if you're the one that put all those miles on it, then you're doing something right. Just keep doing what you've been doing. Regular oil changes, tuneup, timing belt, cam/crank seals, etc.... Don't forget to change tranny fluid and differential fluid every so often too.

If you haven't replaced your vacuum lines, you may want to do that, after all, rubber wasn't designed to last 16 years. Be prepared for the need for new valve cover gaskets. If you haven't replaced them already then odds are you will need to eventually.

If you start to lose oil (mine at 243K does) then do a leakdown test and determine where it's losing it (whether you need new rings or valve seals). If you're losing compression then a leakdown test will also tell you where.