Although I'm pretty conservative about securing the boat to the trailer (I use a pair of transom straps, one gunwale strap, one bow eye strap, in addition to bunks - not rollers - and a bow stop with mechanical winch and safety chain), any discussion about boats bouncing up and down has to consider the fact that there are two moving objects - the boat and the trailer - and that the goal is to keep them from separating.
If the boat weighs more than the trailer, seems to me you aren't strapping the boat to the trailer, you're strapping the trailer to the boat. The same straps that keep your trailer and 3,000 pound boat from bouncing away from each other should do the same when you either trade up to a boat weighing 5,000 pounds, or, preferably, load your 3,000 pound boat with 1,500 pounds of beer, and 500 pounds of fish. In this situation, the weight of the trailer, not that of the boat, would dicate the sizing of the straps.
Boats wanting to move sideways, or forward into the back of your tow vehicle, obviously require a different discussion. But, I think the above is correct when worrying about the boat bouncing off the trailer.