You've gotten responses all over the map, so what's one more...

I fly about 20 hours of actual IMC a year, with a an approach or two
most months. All of this is hand-flown. Because I never turn on the
A/P in IMC, any shortcomings in proficiency are immediately obvious.
Also, I don't really feel like I'm getting enough IMC time to be giving
any away to the autopilot.

I find that this is enough to feel comfortable with the routine tasks
of flying IFR, but no reasonable amount would be enough to be
comfortable with the abnormals - engine failure, GPS failure, gyro
failure, etc. For that reason, I do recurrent training every 6-8
months, and this is typically 5-10 very intense hours.

I used to do more recurrent training (more frequently) but I find that
as the years and the hours accumulate, the skills take longer to
atrophy and less time to rebuild. I'm a firm believer in training to a
higher standard than the worst likely emergency because skills WILL
atrophy some. You probably won't be able to do it right out of the
gate, but you should be aiming for being able to do a night circling
NDB without moving map assist, partial panel, to a short obstructed
poorly lit runway. And if you're in a twin, you should do it single
engine.

My general recommendation is a 3-10 hour recurrent training cycle
(depending on the complexity of your airplane and its systems) on a
regular basis. I think every 6-8 weeks makes sense for a novice IFR
pilot. Once you accumulate your first 25 hours and 25 real approaches,
you can probably back that off to a 3 month cycle. At 50/50, a 6 month
cycle becomes reasonable. And once you pass 100, you will pretty much
know when you need it as long as you are flying IMC regularly. I find
that a year is still too long to go for me. I went 10 months once and
it was too long.

Michael