don't know if I can add to this discussion, but I would still like to point out that Agfa Rodinal is not a fine grain developer. It's sharpness however, is outstanding, and I guess that's why people like to use it.
As far as exhaustion in 1+100 dilution, I have never experienced it, since I always use 50% more developer solution than really is necessary for my tank.
I have never tried to develop under 68*F, but will give it a go and see if there's an improvement.

Personally I use Rodinal only with ISO 25-100 films. Any film over ISO 100 I try to find alternatives.

I tried FP4+ in Rodinal, but like someone suggested, I too shot it at ISO 80 to get some more shadow detail and slightly reduced grain. It was a fine combination.

Currently I'm using the Efke line of films, and they all work great in Rodinal and even better with Tetenal Neofin Blue.

Anyway, hope this helps,

- Thomas

Saint Paul, MN