However, a there may be a downside (if it is considered one), which is having 60 tables inside one single database.

Man, don't sweat the small stuff. Even if MySQL is considered a toy by some people, 60 tables is barely starting to get warm. I wouldn't even begin to worry until there were a couple of thousand, if they're all part of the same application. (Well I would for reasons like replication and hot backups and other such issues, but I suspect that this is not pertinent to the discussion).

It seems to me that it must be quite possible to write a query that returns a result set containing information combined from member info, posting comments and blog posts. In which case it makes complete sense to have them all in a single database. Cross-schema queries should be avoided if you have the choice.