It really depends upon what you want to do. If you are doing anything that is CPU intensive (e.g. graphics) then a cache card should make a significant difference. Otherwise, I wouldn't worry about it too much. After all, why spend a lot of money on a model that's on its last legs. (The IIci is one of the machines that suffers from leaky capacitors.)
And I have to agree with macgreg, the IIci is an awfully nice machine.