I've got a pile of old MacWorlds myself - though only a fraction of what I once had, and nothing from the '80s.
The value of these are highly variable - from worthless to $1,000 depending on the issue and condition. Most are not worth much. I think people are willing to pay some money for an issue especially meaningful to them (to display alongside a particular Mac model, for example). And of course the very early issues can be valuable. The eBay prices can be very inflated though. If you look around locally you can often buy old Mac magazines at thrift stores or garage/estate sales for essentially nothing.
The shipping problem is, obviously, weight. Look at what people are charging to ship those!!! If you really want to try and make money off them, you could try throwing them up on eBay, but the international shipping from Brazil is going to be pretty expensive...