I always get 'agreed pricing' and then take that to my broker to shop around for me. I usually find that most years he'll be able to offset premium increases by shopping and usually get better coverage for the same dollars.
The main reason I go with agreed value is the fact that I find it costs 10k to fit out a vehicle. Water proofing/rust proofing of the floor, carpeting all surfaces, shelving, install etc. That way I can specify what I get covered for.
Like Gary says, if it got written off or stolen, partiularly if it was an older machine, I don't want to be in the position of having a payout of $2500 in my pocket and no machine. Downunder, there isn't a ready supply of second hand machines so more than likely I'd need to consider a new machine and $2500 won't buy anything here. A 'baby' machine like Legend XL, PowerClean Liberty, HM 421 etc START at $30k and upwards.
John