Mike,
The chairs are standard metal folding with fabric seats and a small fabric back near top of chair.
I like the "padcap" idea. The VS has a brush head with two brushes that scrub in opposite directions and dispenses foam. It weighs 14 lbs and is great for a few chairs and sofa but 500 chairs??? Could be a good opportunity to beef up those flabby arms

With the VS you use the brush to clean and then vac away foam/dirt, just can't do both at the same time. Could just spray, brush and wipe that might do a good job and save time.
Bill,
I have a drill but it's with one of my kids! I'm thinking of buying one with the brush head for this job. might just have one of us use the VS and the other the drill brush. That Cyclo looks like a nice piece of equipment. Kind of hard to justify with Winter just around the corner.
Sully,
I've got a step son and will use that for the really nasty chairs.
Mike,
I'm going to check out the furniture dolly, a production line is a great idea. I'm trying to get the chairs done in under 2 minutes. Prespray, was that EG or an upholstery prespray?