What do you get when a ton of Fine fire elementals get together? 16 RHD of bad monster, that's what. Yes, being a Fine swarm does come with some advantages, but having literally nothing other than +12 dexterity, a fly speed, and a 7d6 swarm attack worsens the deal somewhat.
Given its lack of versatility, advancement options, and general power, the cinder swarm is not worth +0 LA. Perhaps give one aristocrat levels and get a brief laugh out of it.