I agree 100%. But that the Democrats would use this (or perhaps even instigated it) is typical and predictable. Republicans in both leadership and on the ground would be expected to demand Foley's resignation - he just beat them to it.
Should the Republicans have stonewalled it? I don't know - it might have hurt the party even more had they done that. Or perhaps it might have shut the Democrats up. I'm really up in the air on that one.
The Democrats hoped they would have. Foley resigned because at least he has the dignity and decency to do such a thing. As you said, Foley beat Hastert to the punch, which suggests he wasn't pressured out.