My experiences this winter have shown that it doesn't have to be cold for the benefits of winter tyres to make sense. As I said earlier, the additional surefootedness when it's wet and greasy is noticable. Also my "best" wheels have been kept away from the salt, crap and tar spots for a few months.
Even with the temperatures being higher, tyre wear hasn't been an issue. Maybe because out in the sticks, speeds are generally lower than for those people that spend a lot of time on motorways, so the tyres don't get as warm.