The alfa diamond flat spokes only come in 17"s I'm afraid. Cleaning is all relative - they're easier than mine, and probablyy easier than the 18" horseshoes too. The diamonds are really flat, so dirt on the sides won't show.
One drawback - if you scuff them, you can't get them refurbished in diamond - only matt. If you only refurbished one wheel, it wouldn't match the others anymore, so you'd have to do all four.