It's really an issue of SPLs. If you're going to be stealthing rock concerts or anything loud like that, the SPLs you'll run into at those sorts of shows will be in the range above generally what the CMC-2s are able to handle on battery power. With the phantom power, you increase their natural ability to handle louder sounds, and as a result your recording's going to see a jump in quality.
Of course, the drawback is that you have to deal with the bulk of the Samson PM-4 XLR connectors (part of the phantom power kit) and the increased size of the PS-2 instead of the 1/8" mini jack + the small battery box. The phantom-powered CMC-2s & the PS-2 can absolutely be stealthed, but since you're just starting out it's hard to say how comfortable you'd be with doing that. If you're fine with bulkier stealth items, then yeah, I'd go with the PS-2 and the phantoms like pfife said.