Before I got my Elise, Silver_Surfer would always harp about weight in the car and I thought he was insane... well more so at least. Now that I have one, I see why there's so much hype.
There is some weight to be lost in the car still, but you'll have to ask yourself... will the car be as livable as it was prior to the reduction. Also, there will be a point where you'll be tempted to use exotic materials for this weight reduction as well. As we all know... exotic = expensive.
'05 CO Elise Mods: Yes
'01 NFR S2000 Mods: No