Hey,
I have been training in the pool for triathlons for nearly six months now, but about a year ago, I came to the same realization as you. I bought ear plugs and nose plugs and worked on what head down would feel like as well as sit fly. I can say that it has helped me A LOT!!! Maybe not 360's or anything, but having the ability for me to have something besides free fall for muscle memory has saved me money and time. I think the pool has a huge influence on serious skydivers, not those who complain that its too unrealistic.
Its the poor mans wind tunnel..and pro FF outthere will agree, because I have asked them first hand..keep what you doing, up. : )