Mike your addition of a switch and continuing through the tunnel is a great enhancement.
The switch too the right on top can throw the switch too its left opposite creating an in and out figure 8. One could also add a crossing guard technology which was available at the time. This would allow 2 trains to run stopping and starting for each other at the throat created by the 2 switches.
One can do both by wiring the controllers with a DPDT toggle switch. One side throws the switches curve to curve straight to straight. The other side curve to straight and straight to curve.
On the lower inner loop a right turnout can replace the curve on the right inside the tunnel and connect to a left turnout where the dead end was. This way with 2 trains on the lower level one can alternate inner loop train to run on new middle loop with the throat or outer loop train to alternate between outer loop and middle loop with a train running on the middle loop. With trains running on the outer and middle loops one can drop a motorized car onto the middle loop for more action.
A pair of 022 switches can be placed near the signal bridge to create a double crossover with the middle loop. Never tried this on a 022 switch but have seen in Standard gauge where the turnout portion of the curve is cut in half and joined with another switch cut the same way to allow for tigher track spacing.
A 22 1/2 cross over can connect the middle and inner loops creating a figure 8 with a throat to the outer loop.