Does anyone know how much the 253,000 email addresses (userbase of threewords) could be worth to a company that runs another social platform?

I imagine that, regardless of whether threewords continues to grow, a related service (like formspring) could add threewords functionality to their own service, then email the threewords userbase letting them know what's up, and re-engaging them..

Is the response rate for those kind of emails pretty good, or would that not be a huge factor in the sale price?