I can only imagine sending an invoice today to my three top clients with "5 Hours Refactoring Bad Code That is Working But Could Be Better Looking....$400".
There is just no way I would get paid.
Unfortunately, I have interests outside of working on code that mostly preclude me from sitting for hours happily breaking-and-then-refixing code that is currently working ok and that I cannot bill on.
Hell, just keeping up to date with the unreal pace of change that is occurring in software right now is almost a full-time job in itself, much less fixing old stuff that is going to go away soon anyway.