I'd certainly agree that if a quick fix starts to accrete complexity, that's good evidence that it's time for a rethink. "ad-hoc modifications", I'm less certain about. How often is this happening? How much effort do the modifications take? Would the modifications still be needed given a "done properly" version (my experience: often yes). Would they be substantially easier?
It can go either way, and I'm certain not trying to argue that quick fixes should never be replaced -- just that trade-offs should be considered.
1. Put a quick and dirty script in to quickly solve some immediate problem
2. When that quick and dirty script stops working, instead of putting a proper solution in place you either add another quick and dirty script in to plug the issue or you modify the original quick and dirty script in some ad-hoc way
3. Repeat over and over again
And then you end up with some impossibly complex Rube Goldberg machine.