No, there is no performance penalty at all. Neither are ERC20 tokens mined nor do they need more storage when there are more of them. No matter how many tokens there are, they are stored as an uint256, so each account needs exactly 32 bytes storage.
Actually, I think it could even get a bit cheaper: usually you would transfer much larger values (since there are more tokens in circulation). Since parameters of transactions are encoded as big endian in transactions, you could omit lots of unnecessary zeros which are needed for small value transactions. For example, this transaction would only need to send
c67275801f87c00 instead of
0000000000000000000000000000000000000000000000000c67275801f87c00. This will reduce gas costs albeit by a very small amount.