I still have some surplus BMW branded ragtop cleaner and protectant that I bought when I had my Z4 roadster. Which I have used on the Mas Spyder with no issues. These other products are supposed to be pretty good, although I have never used them: http://www.raggtopp.com/
Recently I had work done on my black topped Spyder at the Maserati shop in Atlanta. Part of the deal was a wash for the car. Afterward, the top looked good so I asked how they'd done it. No soap or cleaner involved just a pressure washer with plain water - again no soap. They also pointed out not a really high pressure machine. Since then this has been my method. Works good - just don't get too close to the top with the wand.
I haven't used any special cleaners or even soap - just plain water.....but one thing I stumbled upon was to drag a folded microfiber towel (large size used for drying) across the top in long pulls from one side to the other. The fibers seem to pull dirt out and leaves a suede-like look afterward. I'd imagine that some sort of UV protectant and water repellent wouldn't hurt. I'll check out the RaggTop products. Thanks.
Other than that, I wash with a microfiber mitt and carwash soap when I wash the car. I used the ragtopp stuff, which seems fine, but I'm not sure if it actually added any repellency. Didn't hurt though.