I've had four MasterCrafts over a period of 20 years and have on occasion bumped over (briefly started) all of them and have never experienced an impeller failure. When I do this procedure it's not at the ramp but in the driveway before I leave for the ramp and typically after the boat has not been started in a week or two. Bumping over your boat to see if it'll start while on the ramp is way late in the process. This being said I've never heard of anyone losing an impeller over a 2 second dry start and I've been around these boats for a long time. The failures I have seen have typically been due to an obstruction of water flow to the pump or poor maintenance.
If you've ever winterized your boat and pulled the impeller you'll notice water come out of the housing when you break the seal. I just winterized a boat last weekend that hadn't started in 2 months and water came out of it. This amount would be plenty of water to lubricate the impeller for a 2 - 3 second start. I too change my impeller every spring and it's been very rare that the old one has been in less than very good condition. I have seen no noticeable adverse wear from the 5 or 6 "dry starts" that I've preformed during any season.