I dumped Allstate when they jumped from $600 to $850 every 6 mo. (Michigan, no-fault state, polices only run 6 months with most carriers). Allstates justification was this:
"Well, you know, Intrepids are not cheap cars to insure!" I thought to my self, "If that's all you got to say, I need someone else.". Shopped around and got it back down to $600.
I too have a clean record, no accidents, tickets, comp claims for 25 years.
The one lesson I learned is don't feel that you have to remain "loyal" to any company. I was with Allstate for 18 years, they were VERY reasonable for a long time. I'm sure they didn't feel any loyalty to me when the jumped $250 without reasonable explaination. Now I'm keepin' the $500/yr. in my pocket.