A nice looking desktop isnt really so much about color resolution. Granted they help for people who are artistically incompetant, but its not essential. There's just as many horrible looking desktops that are high res/high color as there are nice ones using lower resolutions and lower color depths.
Another thing to consider is that the Workbench screen isnt all a person will use when using an amiga, so if you use too high a resolution and color depth you'll quickly run out of chipram when you try to use other software. And this is even when using FBlit/Ftext/etc.
