In my fantasy world magic allows for low-level blunt-force, object density manipulation (Impact/collision manipulation, damage amplification). These magic spells require physical touch, and they can't be used on living things so no enhancing the human body for example. These two spells combined would allow the user to increase and amplify the damage taken by the target, or to put it another way it would allow the user to manipulate the force/overall intensity of impact making an object easier to break/destroy or a person easier to defeat (smash into a bloody pulp). From an outside observer it would appear as if the weapon user is endowed with super-strength, it would basically allow someone to simulate super-strength. The way I am picturing it, it would allow for soldiers to ditch metal based swords and other bladed weaponsfor cheaper magically enhanced blunt weapons made out of even the most rudimentary of wood for example. With the added excuse of metal being harder to manipulate through magic due to some intrinsic property, this would render metal weapons overly expensive, redundant, maybe even useless. People would eventually turn to wood to make weapons, due to being readily available and cheaper. I assume combat style would be less slicing and more smashing, allowing for a more blunt trauma type of warfare (Also suppose shields would become useless, as people would rather dodge than risk getting smashed to pieces, speed thus becoming an important variable).
Well, at least not how you described the magic system. If the magic can only be used while touching the object, then there's a metal-based bladed weapon I can think of that's incredibly useful on the battlefield which isn't in contact with the wielder when touching the enemy. That is to say, arrows. Arrows, and artillery in general, is a fantastic force multiplier when used correctly, and thus metal-based weapons won't be completely ignored.
I would agree with your assumption that metal personal weapons - i.e. swords, maces, lances, etc., the kind that you are holding onto when you use them on others - would definitely be replaced with wooden weapons. However, not necessarily battlehammers and clubs. Actually, I'd think the weapons would be replaced with gigantic longswords straight out of fantasy novels. If they weigh less and are stronger, you get bigger weapons. And while blunt trauma is tempting, remember that impact is just force / area, and thus not only will your blunt trauma be better, but your cutting edge on swords will be improved as well. Not to mention that swords can cut poles, so given that the combat will shift to giant weapons, everyone will be using sword-like weapons, because using a blunt hammer is asking to have a sword-user cut it in half. And then you're dead.
And that is also why shields are going to be gone. I'd imagine that magic-boosted shields will provide a defense against the magic-boosted weapons, but when you can wield a sword the size of a door, who needs a shield? Not to mention that you can take a set of wood armor and apply magic to that.
Congratulations. Guns are super easy in your world. You no longer need gunpowder to launch projectiles. Just have the hammer hit a metal ball with its mega increased force. The hammer on the gun is constantly in contact with the mage and the ball takes all the force and becomes a destructive force all its own.
For that matter, ballista, catapults, etc. gain a lot of extra power as well. Just apply a force enchant to the launching mechanism and get rid of bulky counterweights.