Simple code has almost always good performance. If the code is simple enough, fixing all the performance problems with just one tweak should be easy.
I suggest the title be changed to RefactoringForSpeed?. Personally, I think some people obsess over speed.
Sometimes this is true, sometimes not.
I've seen code where this was true - adding a CachingVariable? to keep the results of an expensive function call.
I've also seen code where it wasn't - the simple code was making naiive assumptions that were only justifiable in the small case. Getting there from here with ReFactoring just wasn't possible, it needed a rewrite of the core object, plus updating every client call.
-- BevanArps