I agree with fenders, especially if you add a long mudflap under the front one. I also lube my chain with "wet lube", which tends to resist a relatively long time in the rain or snow; however, when comes Winter, I sometimes apply grease (yes! others use very heavy transmission oil) because it lasts longer under salty spray mist. For Winter protection, I also coat the bottom bracket with grease.

Drivetrain cleaning is not too much of a chore. I get the crud off the derailleur's jockey wheels every month or so (more often in Winter), and I usually have to clean the chain once in Summer and 2-3 times in Winter. I clean it the lazy way, with WD-40 and a brush. At the same time, I check tires, front brake pads and other potential source of problems.

Twice a year, I swap tires: 700x37 studded (1 bike) or knobbies (others) in Winter, 700x32 slicks in Summer. This is a good time to check tire wear. Full fenders have one drawback: it's easy to wear them out without knowing it!

As for actual bike cleaning? I usually wash the bike every spring -- whether it's dirty or not -- and sometimes wipe the bike tubes and the underside of fenders with WD-40. The latter is a sort of water repellent and I find it reduces the amount of stuff sticking under the fenders. How often? Maybe every 2-3 weeks in Winter and 2-3 months in Summer.