There are only a few sizes I wear to dullness...every 2 years or so... I just get new ones. I can't even justify a Drill Doctor and they're low cost. Mind you, most of the drilling I do is done with those combo tapered/ countersink gizmos from Lee Valley... Then there is one size of forstner style bit, a 35 mm, of which I own 3..and I have those sharpened professionally.
I had so many dull bits it was redicklus. ;~) If I only used the bits for wood working I'd probably only buy replacements but I often get into other stuff. And then I break bits at inopertune moments and those can be revived with a sharpening with out having to make a special trip to the store.