Thanks in part to the advice given earlier in this thread, I went ahead and pulled the trigger and bought the Zeiss 50 2.0 ZE Macro. UPS showed up yesterday afternoon with it and I had a little while this morning to test it out. So far I am very impressed with the image quality. The focus ring is very smooth and has lots of throw which is wonderful for closeup fine-tuning. I was a little surprised at the infinity end of the focus range, as compared to some of my Canon lenses. I did a quick set of distant test shots comparing it to my Canon 24-105 set at 50 mm. The Canon, when manually focusing, goes beyond infinity, but the Zeiss hard stops right there. I had a little trouble being 100% sure what I was focusing on (maybe 50 yards away or so) was right at infinity or just a smidge back from it. Shots came out razor sharp so I guess I got it OK.
On the distant landscape (mountain) shots the Zeiss is sharp edge to edge from about f/2.8 on, unlike my Canon 24-105, which gets a bit blurry near the margins when pixel peeping at 100%, regardless of the aperture.
Here's a couple shots I took this morning in the garden. Same scene, one at f10, showing the entire flower and prickly bud in razor sharp detail, the second is at f 2.0, showing the creamy blurring of the background.