I am wondering if the keel reinforcing piece with all the epoxy that fills the void between the v of the hull and the flat piece is really needed or a matter of super overbuilding. I followed the directions since the designer certainly knows more than I do, but I still wonder........
Does any other design fit in a piece inside the hull to strengthen the hull from the inside?

If you are glassing the inside of the hull (or taping the stems, inside), it's a bit tricky to work the glass cleanly into the 'V' at the ends.
IMO, inside stems and/or epoxy fillets are as much to ease the glassing steps as to add a lot of strength. I use the lightest wood I can find (luan 'bending plywood' cut into strips and laminated) for inside stems. Lightweight cedar is another option. Epoxy fillets are excellent but a bit expensive, and I have to get the consistency right to avoid sags as the epoxy cures (and warms up). I usually add small fillets even if using internal wood stems. Some folks who are handy with a gouge have done a nice job of 'hollowing' the inside of the stem prior to glassing.
Lotsa options... ;-)

These things do add weight, but the inside ends are usually very awkward to access once the boat is finished - not the sort of place I'd want to do a repair.