The HD Denim cleaner was the best I found for spot cleaning - that being said, I personally would agree with you that Denim Black looks killer but I thought the bike (13' Fat Bob) never looked as good as it did on the showroom floor after I started riding it - I went with the Vivid Black on my current bike.
I use S100 or dawn dish soap for a total bath. for after rides cleaning I use a foaming aerosol window cleaner. And yes my bike is a little glossier than when new but each bike takes on its own characteristics. I love it.
I used glass cleaner on mine, easiest color to keep clean by far. Wizards makes a flat finish cleaner also but 99% of the time windex worked great for me.
I use products from Chemical Guys to clean my RGS. They have "meticulous matte detailer" a matte finish wash, and a matte paint sealant. I have also used the HD product and it works well.