You should give them a third and fourth chance, too. The problem is this - when you're using the mics to capture ambient sound, there are too many variables left openthat can affect your chances of a good capture. Not only do you have to deal with drunk morons, there's also a strong chance that the audio sound will "change" from night to night (even if it's the same band playing a multi-night stand). It could also be as simple as you couldn't get to the sweet spot and had to stand 3-to-4 feet away killing your recording.
I only have one recording where I was able to use both the cards and omnis within inches of each other and this was on a light stand, flying at about 9 feet outdoors and too far away from the source. Both recordings sound faulted - the omnis sound distant and the cards sound artificial. This would be far from ideal as a fair comparison. What is better comes down to personal preferences (much like clothes or food) -- even with drunken idiots, I'd still prefer the sound of an omni capture over cards... I rolled on a show last night where it was a signer-songwriter opening and the crowd was noisy. The cards would have deflected the idle chit-chat but the resulting recording would sound "fake" to me but the talkers would be less prevalent. I haven't used the CMC-8 omnis but there are some people on here that like the AT-943/o (again, personal preference). The whole "what mic do I use" I liken this way - if it's a small club (say 300 people), and you can mount above the crowd and/or be closer than 10 people from the stage (and in line with a stack), run the omnis. If you're stuck further back in the room (by the board), then the cards might be the better solution. I usually bring both options with me and figure it out when I get there.
As for the SP battery box - assuming it's a 9V box, it should safely power either mic. Whatever you do, don't try and record a rock show without a battery box - you've experienced first-hand what happens.