Much progress has been made!
I picked up a solenoid (and some other bits to be talked about later) at Ax-Man Surplus on the way home last night, and after dinner commenced to some informal strength testing.
The new solenoid didn't have an obvious voltage rating on it, but I believe it was a 12 volter, just like the units that came with the POTC game. I hooked both up to my 18volt drill battery, and I was surprised that the Zizzle solenoid was stronger than the one I picked up. I had hoped that an easy swap out would give me stronger flippers - no such luck.
Both units are the same size and have the same bore and plunger sizes, so, on a whim, I tried swapping the plungers to see what would happen. I was pleasantly surprised to see that the new plunger in the old coil was significantly stronger than any other combination, including the OEM solenoid! They are made from different materials, so I assume that the new plunger is more ferrous, or has a different crystalline structure that helps it to work with the coil better.
I'm going to conduct some more scientific tests to see just how much better it is, and to validate what my initial tests seem to indicate - but I think I have a good solution to solenoid power increase without having to mess around with any wiring, PCB hacking, or power input. That makes me happy. When I do conduct the formal tests, I will publish that data here as well as any material information I can find on the new cores so others can easily up their own Zizzle's power.
The old plunger with the flipper assembly still attached, and the new plunger that I plan on using is on the bottom:

I also started to do some initial layout of the new playfield, using my existing POTC playfield as a base. The fiberboard is easy to drill and cut holes in, so it has been working pretty well. I wouldn't really call this a whitewood stage, more of a graywood...
I have a few of the main features placed already. As i said earlier, I plan on reusing most of the stuff on POTC, but I want to re-theme and move some things around to shake it up and get away from the shoot-up-the-middle play that was the focus of the original layout.
It is very challenging to move things like ramps around and find good places for them where the shots will work and the ball won't get stuck - all while using pieces that were engineered for a different layout.
Here's a (more or less) top down of what I have so far:

A player's perspective of what I have so far:

And a close-up of the top of the playfield, where I have been working so far:

What I've done so far is to cover old holes with electrical tape, and re-plug some holes with lenses so that I can test roll the ball to make sure that, at least in a rough way, the new shots are viable. When I have everything where I want it on this field, I'll use it as a template for the first whitewood, and that's where the proof will be in the pudding. I fully expect at that point to have to do a lot of tweaking, just as any designer would.
I think the specific theme for the game will be Rise of The Seekers - with Starscream, Thundercracker, Sky Warp, Thrust, Dirge and Ramjet all present on the field. The other option is Rise of Bruticus, with all of his component toys represented as toys on the field somewhere.
We'll see where the layout goes, and then I can figure out what will fit.
That's all for now - more to come soon!
Larry