Just do one. It either works or it doesn't. Unlike those lazy folks out there, nothing ventured, nothing gained.
Definitely randomize your templates. You can randomize your own unique templates easily as well.
I have some input based on personal experience. If your DOM is 10% different, that is enough for Google to skip you in a mass ban. It doesn't guarantee you will evade manual inspections, only quality content and genuine differentiation can do that.
Don't keep nav common, don't keep footer content common, and don't keep external filenames (css for example) common. Change class names as well. I work above and below the body tags usually.
When you've done it once or twice, it's under an hour per site. If your sites are worth more than one hour of wages to you, then it is an easy economic calculation.
if you're using something like Wordpress or an engine with a lot of templates, it's easy to keep them random. The bad news is, not all templates are equally good on the user side, so there are tradeoffs if every node in your network is expected to optimally convert.
+rep
try template spinning much like article spinning ie your stylesheet will look like this before you spin a template.used [] instead of {} as it is used in css.Code:[#col1|#column2] {width:[100px|125px]; float:[left|right];}
That's very cool, randomize classes as well like guerilla said.