I'm with you on Kronwall. Alfie hasn't been particularly over-worked this year so I'd keep him in if he's healthy.
Datsyuk is a little different as I'm seeing it. We need him to be at max capacity come Boston (or PIT) and I'm thinking resting him is the opposite of what he needs.
He's been okay and contributed, but really hasn't looked like his usual self at all since his return. This is to be expected, so I'm not trying to sound alarms. A couple more games to get his rhythm back before the PO's is the best thing for him as I see it.
This assumes that it is in fact true that he can't exacerbate his knee troubles by playing, as is being claimed.