I have a little over 3 miles of dirt and gravel on my ride. My usual routine is to once a week clip a Park Tool chain cleaner on and do about three complete cleaning cycles, changing the cleaning fluid between cycles. If need be I take a brush to the cassette. I then relube everything and wipe off any excess.
Once a month I pull the chain off and give it a soak in degreaser and go at it with a brush. At that point I also clean the cassette and double check the derailleurs and lube all the pivots. I use Tri-flow throughout and it seems to work fine for me. I get about 2000-2500 miles on chain and cassette with this routine. Still not exceptional mileage, but it is good enough for me. At some point I realized that more time cleaning just wasn't worth it given the price of a cassette and chain.
The other thing that I have started doing is washing my rear wheel down at the end of the day. I have worn through two rear rims. Each lasted only about a year and that is far too short of a life span given their costs. On the advice of my LBS I now try to wash the grit off every night to reduce rim wear from braking. It's probably imperfect and not entirely successful, but if I can extend the life of the wheel by a reasonable amount then I will be happy with the extra work.