Very variant spell magic

[Whitewings]

The standard spell magic system in GURPS assumes that spell casting is relatively common and magic items rare in the extreme. This is a perfectly valid setting assumption; I do not speak against it generally. But I have a setting in mind that's almost the opposite: magical power objects are by far the most common method of performing magical feats, and simple casting is uncommon at best. So what would be the least change needed to the spell magic system to express this element? I keep specifying spell magic because I like its structure and I know it best, and because the other systems, other than Magic as Powers, seem to be based on the same "casting common, items rare" assumption.