Floppy, Since your dog eye sight and other conditions that your dog has, maybe it is in the best interest for your dog..NOT to be a hunting dog. You don't want to make a mistake and put your dogs life in jeapority, just because you guys want her to be a good gun dog. Yes, spaniels were bred and they will always have that drive to hunt, however like you stated over breeding has deminshed the breed.
I used to own a spaniel as well. I never hunted him. He did have that drive mentality...brought me some dead birds that he caught while out in the yard. I would still take him hiking, exploring, etc. He loved it.