Thanks for replying, was thinking I was the only one with this behaviour, have submitted awhile back to Apple via Bug Report so might get sorted.
From what I have discovered, if you delete all, then the next time you restart or login 8 keys are generated (2 of each), leave them alone and do the same results in 4 more added and so on - if you are in the habit of restarts or logins that can soon mount up.
If all keys are deleted iMessages still appears to work ok but that might be down to the fact that they are used when logging in, so while the Mac is running they might not be required (not sure about that though).
What I have discovered is deleting all but the last ones created (the bottom ones of each type are the new if you have Keychains "Name" column set to "^") although only adds 4 more on restart it causes issues with iMessage and FaceTime - 1st iMessage text appears to fail, others thereafter ok and you can not receive calls unless you first open and close the FaceTime app. Both of these can be avoided by deleting all but the first ones created (the upper most ones of each type), then on restart 4 more are added but iMessages and FaceTime appear to work from login as normal. Not sure if this proves that although new ones are being created the old are still the ones being used!
Anyhow, I try not to restart my iMac too many times and if I do I will periodically go into Keychains and delete all but the first ones created - maybe it's linked to the lack of password field box issue when you run Keychain First Aid, who knows, but both are reported to Apple. Wouldn't go a miss if you all do the same so Apple appreciate it might not be an isolated issue - think more might have this problem than we think if they look inside keychains.