Specifically, I am interested in if the Power Boost power (from the Prometheum Exxet) could interact with an item that has the Spellcasting power (though there may be other cases where interactions could occur). It is not immediately clear from the text.
There are two cases to consider:
A spellcaster with the modifier uses the item.
An item is created with the Spellcasting power and the other modifier.
I suspect there is no official ruling on this (as with most of my other questions, in fact), so I will accept subjective arguments.