I don't think there has really been any effect. The vast majority of users don't seem to use sigs.
I am a member of several forums for other interests that I have and participation is not what it used to be in any of them. Dilution I think as there are just so many avenues now such as Twitter, FB, Reddit, etc. and really there probably is negligible growth in internet use as everyone has been on for a while.
As for real estate in particular, just check Google Trends as see the dive in interest in "real estate". Not going to see much growth when interest is waning. The internet boom is over