Even using spades, isn't it best to drop some solder on the wire? I usually apply a small amount to the wire to make sure they don't fray, and then solder the spades directly to the terminal or just the bare wire. Not that i am any good at it, but it has generally (with the exception of my apogee issues), worked fine. That said, I would desolder that wire, clip off a piece of each end, and re do it with some shring wrap and electric tape this time.
Daryan