I got some brass and stainless wire brushes to use with my die grinder, only tried a small patch but both work very well and certainly easier than by hand also very handy for many other parts, my footpegs and brake lever are like new
By the way I only used it on the cast finish part of the frame I wouldn't recommend using on rest of frame!

I've used alloy wheel cleaner but don't leave it on for to long

I also used alloy wheel / mag cleaner, no ill effect but didnt really help clean either... my experience is WD40 and a slightly abrasive kitchen sponge did the trick