Frontier changed their cancellation policy as of June 2nd. There is a $99 fee to cancel now, regardless of how far in advance you do it. It's not waived for 50k (100k gets The Works for free, so they can cancel via that benefit).
Furthermore, I think your refund credit will be one-time use only, so you lose any residual value if you're trying to use it to book the same flight at a lower price.

So the only situations where it makes sense to cancel IMO is:

1. You purchased The Works

or

2. Your flight drops by > $99 AND you plan to use the refund for a different flight where the ticket costs more than the first flight minus $99.