Hmmm, this could be a use for shopping mall parking lots since it appears some of them may be closing.
That's smart. Don't know what the legalities would be - liability BS or whatever - but you're right, there's enough space to do it.
As to the performers not feeling the energy, well, that would make it less fun. But I've been in bands where just rehearsing was satisfying. So if you could do that knowing that people were watching and digging what you were doing...so much the better, right?
It might even provide an opportunity for FM radio-based sound system rentals at the concerts to provide an income stream for the band or perhaps a sponsor.
Bring out the porta-potties, the show must go on!