I think all 4 would add something useful. Ayala is meant to be highly rated, but doesn't he belong to Liverpool? Snodgrass has good feet, and decent delivery from what I have seen, and is there not previous playing for Lambert in Scotland? Lacks pace, but can take a free kick, and we seriously lack decent delivery full stop, so if he is cheap, which he may be due to his contract, it could be a goer.
Holt has been done to death, but cheaply done he gives us something we lack, and scores goals. Old yes, but might be worth it.
Matt Phillips would be excellent. Now Ince has come through there too, maybe Phillips will be gettable so to speak, and Holloway might be on his bike anyway.