That is a great point, but you said it yourself, maybe I need both. And that's MY problem, I can't buy both. I'd really like to have the subject and backdrop separation the 135 brings but these detail shots really mean a lot as well. If it means anything, I have the 60mm macro for for my 60D.
Yes, that means a lot. If you're ok using 2 bodies, then use the 60 on the 60D and the 135 on the FF. The only reason for pause is if you plan on getting the 70-200L II in the future. If you do, I suggest getting the 70-200 II first. There's not that big a difference between the 135L and the 70-200L II at f/2.8 at smaller and the zoom gives you a wide focal length range and better AF (servo). I have both, but I tend to use the zoom a lot more because of sports. The 135 is used specifically for portraits and low light indoor applications.
Perhaps the best path is to get the 135L now and trade in the ef-s 60 in the future to help offset the 100L's cost.