No harm. No benefit. Single wire is simpler.
The only problem I can see is if your speaker cable of choice is designed to be "directional."
Reversing it does not mean harm will come to speakers or amp, but it's possible it would sound better running the direction it was designed.
Richard Vandersteen has long touted the benefit of bi-wire, particularly for some of his designs. The only way to know for sure is to give it a try. Just be certain your not shorting out anything while swapping wires.