True. The other side though is that fringy AAAA big leaguers have less trade value than their playing value since there is a cost to holding down a 40-man roster spot or the use of options. This is one reason that younger prospects get a little extra value if they do not have to be exposed to the various ways minor league players get moved around (waivers, options, minor league free agency, etc.). A Perkins or that other minor league SS we had briefly have little value because their talent level, while good enough to maybe have a bench role, is also talent level that is easily replaced by another AAAA guy.
For instance the Phillies are setting themselves up now to have some AAAA guys with little value. Does a guy like Mark Leiter really have any value if he is our 11th best reliever and 9th best starter. Below him are younger guys that need to start. And above him are guys that have more ceiling that you don't want to lose. So he may get sacrificed in a numbers game at some point.
Circling back to the international guys - yes there is some allure in young untested talent that might have a high ceiling. But there is also allure in 5 years of control which is gone with the older AAAA prospects.