I agree that doing the manufacturer recommended interval services could become expensive if you ride your mtb a lot. I have a engineering/mechanical background and do all my bike maintenance myself. Lower leg service every 3-4 months and full service every 12-18 months. Personal habit is to wipe stanchions clean with a soft cloth after every ride, muddy or not. Then i have also personally seen what a difference these little plastic mudguards make, get one. As mentioned before, not everyone has the tools or mechanical knowledge, but do stick to the service intervals as close as possible or it will become a very expensive exercise. Mudguard and keeping stanchions clean will help stretch the services.