I actually thought the moment where Marion drives off the cliff and into the tree was a good example of how resourceful she is. If you payed attention while watching the movie: just after Marion avoids driving off it the first time (after Mutt yells, "Mom, there's a cliff!), she looks over the side, and the look on her face is an obvious "I've got an idea!" expression. So, she actually saw the tree, and then drove off the cliff to land on top of it, knowing that the weight from the duck would make the tree bend over and put them in the water gently. I don't know about you, but I call that SMART.
Anyways, one change I would have made, that could have lessened the silliness of the fridge scene (or at least acknowledge it), would be to have Indy, upon falling out of the fridge, mumbling something along the lines of, "There's no way that should have worked!" Voila, the inherently implausable nature of the scene is poked at, and tells the audience, "Yes, we know it's ridiculous, so we aren't idiots. We did it just to have fun, and if you don't find the scene funny, then you're missing the point."
I'll try to think of some more...