I agree... a good conversion is a profitable conversion. Someone one time told me about his 0.1% conversion, which is really, really low... that is like 1 sale in every 1000 website visitor.
But the surprising thing is that it's profitable. If you are spending $50 to get 1000 visitors and that makes $100 in return, who'd want to throw that away... right??
But of course, conversion rates can quickly give you an estimate how much you need to spend to get sales, provided you know your niche/industry. I suppose that is what conversion rate is for. And knowing that, you should also work on increasing conversions and not just traffic.