I'm for "Walls and Bridges" all the way; it's even had a Quad release already (it rates 4 ridin' cowboys from me!)The only way "Plastic Ono Band" will sound good in surround is if they do a "Raw Studio" 5.1 mix just like they did for "Imagine". Otherwise there's no point in mixing this album in surround sound.
The songs with the most potential for 5.1 mixes are definitely "God" (which features both John and Billy Preston on separate pianos) and "Love" (which features Phil Spector on piano and John on acoustic guitar).
I would prefer deluxe editions of both "Mind Games" and "Walls and Bridges" as both of those albums have a lot more potential for surround sound than "Plastic Ono Band" does.