It's no less secure. The only thing you distribute to each hosts is your public key, whether you have 1, 2, 3, or more key pairs. If one of those hosts becomes compromised, it doesn't compromise the others because there's nothing they can do with the public key.
The security comes in keeping your private key private. File-based private keys can be stolen, so keep them encrypted! Owning the private key validates your identity, or at least that you're in possession of the private key. I would think that becomes less secure if you have more of them to manage or keep them in multiple places. There may be administrative reasons why you might want more than one key, but I can't think of any good ones.
Also consider using hardware based keys. For just a few dollars, you can get a USB smartcard token that does the required crypto ON THE TOKEN. It's just like file based key authentication except the private key never levels the token, so can't be stolen or compromised. Unless of course they PHYSICALLY steal it from you and coerce you to give up them PIN. AbsoluteTelnet/SSH supports hardware based authentication tokens natively. I can give you more information if you're interested.
Here's a good article I found on the subject:
security.stackexchange.com/questions/400...-ssh-key-for-all-hos
Brian