BM, I am using a copper lauter ring in the bottom, not to dispense the water. I think that I just need to up the temperature of my water to around 185-195.
AJF, the grain depth is pretty good actually, around 6 inches. The keg holds the temp the entire time I mash and I'm not worried about insulating. Might have to start mashing out at 175 before lautering though.
With the shape of the keg, you might be able to get some cross members in there, but then the simplicity would be gone from the ring. I mean, next step seems to be a false bottom, though for that kind of investment I don't mind losing a little bit of efficiency.
All in all, it comes down to being one more thing to try and improve next time. Hotter water, hotter wort, batch sparge and on and on.