I'm with Aviva, and when I enquired about the cost of insurance to fit heated grips and luggage (topbox), I didn't get charged any extra. I did get charged extra when I bought the Fazer, but to be fair it was a far bigger bike than what I'd had before, rather than admin charges.
FWIW, I had a claim on a works policy (also Aviva) after a van decked the bike 10 days after I'd bought it, accident happened Tuesday with the claim settled by Friday, and the bike assessed by the following Friday.
If you're going through brokers, try going directly to insurers (that way you avoid brokers fees etc).