My suggestion to cut weight would have been to make a frame with 2 x 4s turned 90 degrees from what you have there then use a sheet of 1/2 or 3/4 plywood. Then if you wanted you could "clean it up" by covering the bottom side with very thin (1/8") sheet of birch or even cheaper hardboard. You can get hardboard in a 4' x 8' sheet for about $10.00. I also wonder about the dowel rod load carrying. If you framed it with the bench top base with 2 x 4s, the 2 x 4 that runs along the wall could be made longer to rest in the nests you already have.