Privacy is always valuable.
I run a site that provides counter information for League of Legends (http://www.championcounter.com/) and I doubt very much my users will benefit at all from me moving over to HTTPS.
Also some isps have been caught injecting ads into plain text web sites [1]. Do you want more ads on your site that you didn't put there?
[1] http://zmhenkel.blogspot.com/2013/03/isp-advertisement-injec...
Protecting against code injection is actually a fair point though.
Encrypt.
Let's see it the other way: any sane webserver allows you to easily activate TLS, and generating a certificate is both free and easy. What's the point of going back to HTTP at this point ?