The problem that comes up is by the time you hit the tipping point of more cleaning then feature additions you end up having to do the fast solutions to fit deadlines.

I think when you take on the debt of poor code you have to remember that what it will take to fix that problem will continue to increase the longer you are away from that code.

Now I don't think you should consider fixing things for scale poor code that is it's own beast which makes the most sense to handle once you have the problem as you can't really tell what the problem will be until you have it.