Waka,
I tickle them up couple times with the stone before getting them reground (unless they get badly nicked).
You could get them sharpened at least 50 times at your local saw doctors for the price of the tormek with the optional planer blade attachment. I use Tewkesbury Saw Co. - very good service.
I only had them reground only twice in 4 years although they cut mostly softwood.
ike