Interesting, I had to look up what a "flyweight" pattern was. I may not quite understand the concept correctly from the definition I saw though. To me "flyweight" just describes every program ever written in c, or just relegating the functionality of objects to the things that manage them. I don't know if that's right. ..?
Looking at it again, I think I misread that before. You're probably using the flyweight pattern, but that's not what you were describing.
It's basically deduplication. When you've got a lot of objects that are largely identical, don't give every one of them its own copy of the common data. Just keep one copy of each and give each instance a pointer. It's the same way combos work in ZC, for instance; each one on the screen is just a combo number rather than a separate copy of the definition.

Tell that to the stupid compiler.
What I mean to say is that the "root of all evil" optimization isn't high-level design. It's stuff like rewriting a function in assembly to save a few clock cycles. Small things that make the code harder to understand and maintain for relatively little performance gain.