Honing stone? NOOOOOOOOOO!!!!!!!!!
The whole point is that you have to remove some material to clean the face of the grinding wheel, as you litterally have molten metal imbedded in it. Using a wire brush will just add more metal. Using any type of cleaning solution just adds gunk. Using a honing stone might work but I'd be very worried about chiping or breaking, as that's really not what it's designed for, and I'd guess you stand an equal chance of increasing the gunk level in the wheel. You can mail order a diamond wheel dresser from any craft supply for about $15 and shipping. Works well, has a flat surface so gives a good 90degree face, etc. Well worth it.
And, remember, grinding wheels aren't designed to be permanent. They're temporary and wear out, just like sandpaper and the edge of a tool.
Dietrich