| PodoDraken |
Without more information, there are, as seen, many ways to interpret what the OP meant. This is how I see it myself. Having played in a high level game and one of the other players thought that a complete set of gear that kept them encircled in a continual AMF would make them invulnerable. They found out the opposite. So here are the points I get from OP's limited examples.
This means, for a couple of examples, if you cast a spell on them, it auto fails,...
I would assume the OP meant by casting a spell on them would mean a targeted spell. Magic Missile, Flame Arrow, etc. But not area of effects like Fire Ball or Meteor Swarm. This make me think that the magic fizzles out upon touching him, or his clothing/armor. The AOE would not effect them but all around them the effect would still function.
... for example, if they hold a +1 longsword, it is treated as a masterwork longsword for them, but likewise, if you attack them with a +1 longsword, it is also treated as a masterwork longsword. ...
The OP's later example reinforces my first point by the statement that the +1 sword is in contact with him. First by holding, and it becomes non magical, and later when it strikes him, again becoming non magical.
This being said. Any effect that a Dispel Magic or Anti-Magic Field would suppress/remove would not function as soon as it came in contact with him. If the effect is on an item, that itself isn't made of magic, just enhanced by magic, said item would still make contact, sans any magical effects.
This is how I see it anyways.
EDIT: On the question on more powerful or less. That would depend on the situation the person found themselves in honestly. Highly offensive magic area, he would be better equipped. No magic area of area where most the enemies abilities are Extraordinary, looking at the Fighters, not so powerful, but, if he is a fighter himself, is on equal footing.