The cost is quite low for a single connection, but given that Google Analytics is on a huge portion of sites, that adds up really, really quickly. In addition, the additional roundtrips required for the TLS handshake is killer on a high-latency connection, seriously slowing things down for mobile devices.

Given that there really is no privacy benefit, I can't imagine why you would take on that overhead; Google clearly agrees, or they would've turned on HTTPS by default.