Belt sanders or variations like you have were industry standard until 5 or 10 years ago. We used them all the time in our larger shops, on squeegees up to 55" - you need a couple of belts of different grit to do a nice edge and a thick flat glass plate back and adjustable handleholder guide. Like any 'analog' machine, the operator is the difference between good or shitty.
There are two types of high speed 'grinders' :
One has a high speed grinder head that sands the blade
The other is a high speed cutting head that actually shaves the squeegee down.
Encore Engineering in Fla pioneered this, there are a number or companies that make these types now.
The cheaper (!) models of these (you might look into this, you can build these in kit form or from a router) has a stationary cutting or sanding wheel poking through a table top, and you run the squeegee along in a guide. this only works on smaller squeegees. This also requires some operator skill.
The second type the grinder or cutting wheel travels along the stationary squeegee blade, moving up a pube on each pass. This is definately the trick set up in shops, because it reduces operator error because of the automatic advance of the blade. It's pretty expensive new, and of course the bigger, the more cost.
I think you are right on the shaving vs sanding, it's better on the squeegee. I also think most printers still give their squeegees a little buff with 400 even after the cutting.
So is it worth it? Totally. You have to sharpen your squeegees to produce sharp prints and halftones.
If you are getting streaks and your customers are complaining, you can decide what it is worth in the scheme of things.... Me, I have two friends I can visit with 48" belt sander types (one cost $400 used, the other got his for $200 - Canadian$$$!!!! the fuckers), or I have metal handles and can flip the blades when they are really bad, and I built a little hand model I can hand sand a blade with up to about 24". I also keep 20 or so feet of 70 and 75 duro Ulon blade material for emergencies or when I have to whip a surly client.
Depending on how many prints you are running each day, by hand or on machine, and the blade hardness, you will quickly notice nicks that appear, some for no reason (the edge just crumbles) or some because you are printing over a tape edge or some dried in lugie in the stencil, or a protruding register tab that is also wearing a hole in your screen. Some squeegee material is better than others and lasts longer.
Certainly if you are running process colour, you should be sharpening before each run. You may get away with less sharpening, but even with my hand printing table I'll buff a squeegee every 500 - 1000 prints or sooner.
Many shops have dual sets of squeegees - squeegee rubber gets molecularly bent by solvents in the ink and thinners, and needs to rest in between jobs. If you run the same squeegee over and over and sharpen it all the time it will break down faster.
I would suggest if you are interested in stepping up, check the equipment boards at screenweb and sgia, or check with some of the bigger graphic shops in Portland or Seattle. If you are looking for something for squeegees up to 48" or less, there is a good chance someone bought bigger and needs a bigger sharpener and you could pick up a smaller one second hand. Unless they wrecked the machine, the only thing that wears is the cutting bit.
Hope this helps. Next to the screen, the squeegee is your next best friend in the screenshop. (Besides a case of beer and a fattie)