I mostly agree, but only as Casey hasn't had the best season. He's a solid SPL player and carries a goal threat, so I hope having a proper pre-season this time will help him.
I don't see us releasing all 4 of those you suggest. Halliday already has a 1-year deal, unfortunately, and I can see Kettlewell wanting SOD and McGinn. Slattery, however, may well want something different as he recovers.
Spencer proved he was good enough for us and more, no thanks to Kettlewell.
Whilst not a world-beater, Davor did have a hand in our changed fortunes. He's a decent squad player.
I think Vale could go on to have a decent career, but probably not at the English Championship level.