Even if you hadn't already used a power washer, I wouldn't sling daggers. It's your equipment to do with as you wish. However, from my years of experience, moisture is the third greatest enemy of bearings after lack of lubrication and abrasives. Arbor bearings are usually sealed ball or needle type, so you can't dry them by running the machine. If fact, the only way you could try to dry them out is to remove them and place them under an electric dryer or in an oven. To those who would argue that they have used power washers without having a problem, I would say their bearing seals are doing a great job.
As to your painting question, I assume you are asking about the underside of the deck. Some will tell you to remove grass with a plastic scraper so as not to scratch the paint. Others will advise sandblasting. Accept the fact that the paint on the underside of the deck is going to get chipped and worn if you use the machine. I have several decks that are over 20 years old. I use a metal putty knife, hand wire brush, and air hose to remove as much grass as practicable. Then I paint with any non-water based enamel paint I have left over from other projects. Personally, I would never use a sandblaster unless I removed the arbors (to keep abrasives away from the bearings). Even then, a sandblaster will remove metal. Repeated sandblasting will turn the deck into tin foil quicker than rust will.
As for painting the visible portions of the deck, use the highest number (finest) sandpaper that will featheredge the chipped areas. Choose a well known paint brand (Rust-o-Leum is good) and use the same brand etcher (to neutralize rust) and primer.
Accept that proper deck maintenance is a time consuming job.
Before I would use the short cuts of power washing and sandblasting, I would leave the deck alone. I know my views are contrary to others' opinions. But, while I respect others' beliefs, that's my position and I'm sticking to it.