Correct, we don't want to be destroying Disney's speakers. Usually, on the speaker grate is good, it gets you aligned correctly with the magnet mostly (if it's a traditional speaker) and will probably be the easiest/accessible spot, ALSO the most visible.
The speakers in the ground however are a bit tougher and as Horizons said, moving the induction pickup around the speaker enclosure and surrounding area will allow you to find the best spot. Often the best location is a very small area, could be a band equadistant around the speaker, etc. Moving even as little as 1/2 inch or so could make a huge difference.
I have not done any wire recording, BUT it would probably help get some of the music that comes from the speakers way up on poles, like around Boardwalk, or World Showcase, etc.
As we have mentioned many times, induction recording is a very time consuming process. For an area music loop of maybe an hour in length, I'd plan on spending about 4 hours grabbing it. You'll need to find a speaker that's accessible, and then listen to make sure it's pretty good quality. Then attempt to record it and wait, and wait, and wait... You're looking for a pause between songs. That's the starting point, from there you record the whole thing until you hear the pause again and the same song starts. That's your loop point. You can stop and go home and hope you got the whole thing without any problems, or you can come back at another time and record it again.