Regarding the possible (and hopeful) future "excess" donation pool use, if we manage to gain more traction, and thus more donators, there will most likely be a limit on how many N900 cases can be salvaged (even counting people that already have a case AND would be willing to use it).
People selling N90 cases might also adjust their prices at some point if they see a consistent demand...

So if that limit is reached (or used cases become too expensive), I'd rather have excess donations go torwards producing cases.

PS: That's coming from someone who doesn't own a N900.
PPS: I have obviously no idea about how many cases can be had in the wild right now, so this is highly theoretical.
PPPS: It might have been touched on previous posts, but I think it's still relevant to the use of said "possible excess donations".