Solder tweezers are handy if you need to pull off a lot (like dozens or hundreds) of chip parts quickly, but not much better than doing it with two irons, and not useful for much else, so in terms of value for money, a second iron is going to be useful much more often than one iron and solder tweezers (e.g. when you need to frequently swap between two tips). Unless you're expecting to spend all day picking chip parts off boards...