but how much sloppyness is acceptable, on the long run?
In long run no sloppyness is acceptable at all. Quick dirty solutions work only in short time. If the solution is to stay then for your own sanity rewrite/refactor it so it has no sloppyness you know about left. I learned this lesson hard way - not doing so hit myself so many times. If you allow yourself not to cleanup and refactor your code continuously you always end up with Big Ball of Mud which costs (in terms of time/money) way more to maintain.