From what I understood,
Don't do any major to your engine. If you really want, may be a new set of Iridium/Platinum plug set, cables, Max... an air filter. May be u can do a slight exterior mods. But that also... not too much.
Keep your car well maintained, regular maintenance, tune-ups and services, Original parts will keep your car going happy for a long time. It's the best u can do to this car.
Good luck ....