I went throug the same analysis a couple weeks ago. I bought the JDI. Nice DI's for live no matter what. Yea thorough a PA no body will know the difference.
I think it is not a good approach to any kind of live production to take this attitude. I'm not trying to call anyone out here, I just think it is a bad idea to dismiss better sound quality (or tighter timing) because "nobody will be able to tell".
I assume most of you are familiar with "death by a thousand cuts". The same principle applies to sound fidelity. After a certain point it is difficult to make any drastic improvements in sound quality. Most of the improvements get only a mere 1db increase in signal to noise ratio. But if you add up half a dozen little things you get a significant net improvement.
Or to put it in musical terms. Think about that difficult position change you have to make in a certain song. Maybe you have to get from the 12th fret to second position, right on the downbeat. Sure it "works" if you miss it every now and then. So long as the band keeps chugging along. If you miss it every time the measure comes around the song sound tepid. If you nail it everytime the song sounds dynamic.