While the domain obviously does to some degree reflect the service (so isn't bad branding), I don't think it has any value in its own right. Alexa Rankings don't always tell you a great deal either, so the value would be attributed to the actual visitor stats and/or income earned frorm the site.
Assuming that it does draw in high numbers of visitors (which seems likely), there may be better ways to monetise the site, that you haven't yet explored. This would be useful to you, ad any potential buyer. You ahven't really provided enough info yet, to be able to come up with a rough price.