2K or 4K, digital or film projection issues aside, I think the major issue to look at here is the loss of Screen 1 or 2 as a regular movie screen. As a PI24 regular for years, I make it a point to catch anything I care about on screens 1,2,19 or 20. The decision to re-brand one or two screens 'IMAX' is just a ploy to drive up ticket prices, since those screens will command a premium.
I liken it to the current 3D fad - I saw "Bolt" in RealD out of curiosity mainly. I did not think 3D added to the story, or my experience viewing the film. I saw "Coraline" in RealD because I'm a Neil Gaimen fan, and I was interested in how the art design of the film handled 3D. (a review for another time, but long story short I felt they approached 3D quite successfully, and not as a gag) Will I see "Up" in RealD? I don't think so. I'll pay a couple dollars less, watch it on a larger screen and not feel like I'm missing anything.
Will I go see a film in kinda-IMAX just because I can? Nope. I'll continue to pay regular prices and see it on a regular screen, and in that case my screen choices at PI will now be limited. Screens 1 and 2, once they fixed some of the acoustical issues, are great screens - some of the best in Central Florida. Is it worth it to pay an extra couple of dollars a ticket for a somewhat better sound system, digital projection that may or may not actually look better then the film system did, and a screen that's pretty much the same size as the one that was already in the room?
Now, if they built a 'real' IMAX screen, and mixed some traditional IMAX content in there along with the current hollywood releases, I'd be interested. I missed U23D in IMAX, because it played all of 2-3 weeks here before getting bumped. I would love to watch some of of the NASA films without having to go to the space center. It would be cool if Disney re-ran Fantasia 2000 in IMAX once in awhile on property. But taking the IMAX experience and 'shrinking it down' to fit into PI screens 1 and 2 doesn't do it for me. That's not immersive. That's just large - and we already had that!