I think Dolphin is fine for business, not too sure why it wouldn't be. Building up an online community works better f you have some kind real connection and people have real incentives to join...

BTW I tested ELGG before discovering Dolphin and I can tell you there is zero support and documentation for it, I had quite a few emails from people you had tried installing elgg and had lots of problems with and my forum posts went unanswered!