You are a worthwhile target at a minimum that your machines can be used as part of botnets and DOS networks.
Sure, they might not be digging out your bank account number, but since the cost to the attacker of compromising your machine might be nothing more than a few hundred packets, they'll try anyway.
Sure, which is why I mentioned the "wide net". I take reasonable precautions, apply basic monitoring, and take care with what software I'm downloading so that I lower my risk of this. It's not foolproof but it's good enough to keep me from being an easy target, while not sacrificing any convenience or spending a lot of time fortifying my machine.
Sure, they might not be digging out your bank account number, but since the cost to the attacker of compromising your machine might be nothing more than a few hundred packets, they'll try anyway.