You could do the same thing you have just make that bottom transition piece loner. If you have a jig saw you could cut some ply and make an actual curved transition to go from your drop in pitch to the flat. IF you do that just cut some half inch ply one for each side, if you're using scap you really only need it to be like 4 inches tall along the curve. Then just throw 2x4s across it and screw them in. If you go that route put it doesn't hurt to cut a few slightly long and hammer them into place then screw them. Not necessary but it'll make everything far stronger.
IMO the smoother the better but as long as it's not a big speed bump type feel you'll probably be alright.
As far as the plywood thing. Not sure if you're ever built any skate ramps but it's the same concept. Just tie a string and draw a curve on the ply. Like a big compass. The longer the string the mellower the transition. Draw a few see, how they look and then make it happen. IF you get a full sheet(probably $20-25) you can cut them right under each other and save the rest of your sheet. Wouldn't be the absolute easiest fix but it wouldn't be that hard and would be pretty solid imo.
Sometimes you get some pump out of the bottom. It really depend on the length, pitch, and feel. Some people run some pretty mellow drop ins but they're usually longer. It's the balance of getting a good pump at the bottom instead of slowly rolling through the tranny with no pump and slamming into the ground and loosing all your speed.
