When I installed my first rack of panels in 1985, I put them on the roof. Here we get not only pollen [May/June] and dust [always] but also snow in the winter. Don't believe anyone who says "don't worry the snow slides off on its own" as it sometimes does but often does not. I rigged up a pole made of sections of an old tent-like cover my wife had for some crafts fairs, you know, aluminum tubes that slide together so they can be broken down to three feet long or so for transporting. I strung them together to make them VERY long and put a brush on the end. It was unwieldy but worked, if a bit of a hassle. It broke down, of course, to a collection of short pipes.
Then I had to reroof the house, and I pulled the array apart and down to the ground. I decided to increase the array size and to go through the hassle of putting it on the hillside above my house [longer wire runs, increased wire gauge and more weather protection for it, etc., concrete footer to pour and so on]. Major pain, but now I can walk up to the panels and brush them off with a broom [snow] or, few times a year, a soft brush and pail of water to clean off pollen and dust.
I haven't tried the auto stuff, I just bite the bullet and go clean them. Nowadays, from the ground, it is no big deal and takes me five minutes.
But, in answer to the main question, you would be smart to keep them clean. It is also an opportunity to give them a look over. I cleaned an elderly neighbor's for him last year. He is blind and could still tell he wasn't getting the output he expected. During cleaning, I kept an eye out and discovered a place where one panel had a severe burn in the silcon wafer...even a break and cracks in the glass. Couldn't figure out what caused it, but the effected panel was in the middle of the array and was blocking the juice from the panels behind it. I wired around that panel for him and he was back in business til he got it replaced. You could not see the damage from more than a few feet away, and if I hadn't been cleaning them up close and personal I would've missed it.