People like the Quad G5s provided the LCS hasn't taken out the power supply and/or motherboard.  Once the LCS is rejuvenated it will be fine.  I think they will be a good collectable Mac in the future (last of the PPC) and still hold their own for some tasks provided you don't mind a rising electricity bill.

I once recall reading that the single 1.6 G5 is very closely related to the MDD than other G5s.