logfiles, very good and useful instruction and explanation about importing private keys and sweeping option. As you write in your post there is pros and cons for both option, so before user performed such task it should be sure what he really wants. In case user want to keep old wallet then importing PK in new wallet is good option, but realistically increases the risk because PK are then in two wallets.

Much better option is sweeping, when you send coins to new wallet/address, old wallet remains empty and thus the risk decreases. Private keys are most important thing, it is something that which really allows us to control coins on blockchain. Often people think that they keep coins in wallets, but we actually own private keys.

Therefore, I suggest the maximum caution when exporting/importing private keys, particularly when it comes to claim of hard-forked coins. In such case always use sweep option first and then you can play with empty keys.