Personally I'd go for an X1D/GFX (or A7RIII/D850) over the P45 for reasons that people here have mentioned (full disclosure I have an X1D but had previously used an H4D-40). These days I'd take a FF 35mm with eye AF and an f1.4 lens for DOF with portraiture over a P45 but that's just my subjective viewpoint. That being said, OP, if you're just looking for something to stir up some creative juices, have the cash sitting around, and don't mind the limitations of the older tech, go for it. I've thought about picking up a P45+ myself for my tech cam for fun and just to have something to shoot the tech cam with (that's not film) that doesn't cost an arm and a leg.
I'd also recommend anyone looking to "take the plunge" now to wait a couple months. With the next-gen 100mp 33x44mm and 150mp 40x54mm cameras on the horizon, I'd wait to jump into MF until after those are announced or released and see how the market shakes out. There's always a chance that older CCD offerings like the P45 may depreciate further and get cheaper on the used market as they'd be yet another generation behind. The current GFX and X1D bodies will also get cheaper in stores and on the second hand market. That may not happen of course, but I think it's worth waiting a little bit and seeing what happens.
Just my 2 cents, but you do you OP. I never regretted jumping into MF with a CCD sensor when the D800 was out in the wild along side of it, but the MF landscape was much different a couple years ago. When I got the H4D-40, there were no mirrorless MF options available, nor any MF cameras available as capable as the GFX and X1D at the current price points of the GFX and X1D.
Haven't read through the entire thread, so forgive me if it's been mentioned already, but another option to consider if you haven't already would be a Hasselblad-mount P45 with a Hasselblad body and 80mm HC lens. There are plenty of older H-mount phase backs out there these days for decent prices. That way you also don't have to deal with the DF/DF+, and there are plenty of reasonably priced HC lenses out there these days that will perform just fine on the P45. Plus I think you can throw a 120 film back on the H1 and H2 bodies if that's your fancy, but someone can feel free to correct me if I'm wrong. Whatever you go for, I'd try before you buy if you can.