Thanks for all the responses! Lots of variables to figure out. We are insured up to $271K on the dwelling, which seems a little low for replacement cost, or at any rate not too high. Our deductible is $1K, and we could definitely go higher there. We also have $300K personal-liability coverage, which seems a bit much but I guess it's great to have if you need it?
We've never made a claim, as far as I can remember, so that shouldn't be affecting the premium. I'll have to play around with some of these deductibles/coverages to see if it gets much cheaper. We also have our car insurance with State Farm, and our most recent premium notice says that we're getting a $663 home/auto discount and a $474 claim-record discount. I guess that explains why all the quotes I got were so much higher!
That's interesting that an old roof can affect the premium--I had never heard that before. We're planning on downsizing in about 9-10 years, and I've kind of emotionally disengaged from this house (I've never liked it as much as our first house). So I'm sort of disinclined to invest a bunch of money in it. Frankly if the house burned down I'd just gladly take the money and buy a different house, I wouldn't want to rebuild on this lot (it has a steep incline down to the sidewalk that's very annoying to mow). But if we'd have to replace the roof anyway before we can sell, it might be worth doing sooner rather than later for the insurance savings. Thanks again to everyone for your help and insights!