Well there is already no incentive at all to use them. It seems to me that at every level MA weapons (close combat not bows) seem to lower average damage rather than raise it. Basically every 3rd fist attack is interrupted for a weak weapon attack. As you know, even though the reqs on these weapons favor MAs with MA/Dimach reqs they also require a fairly high req in the weapon type itself, 1h edge, 1h blunt or piercing and you must also raise weapon Inits to even devisors of your phys init. This can be expensive in terms of IPs and basically only accomplishes lowering your average damage and disableing your special attacks. Spending all those IPs on weapon skills should be to the bennefit not detriment of the ma. Here are my suggestions.
1. Increase their damage range to make them 10-50% better than fists. Note, if you have a MA special that does say 800 hp damage every 40 seconds you need a sword that does 80 average a hit to break even. Weapons don't need to be better than MA specials, but they should be an alternative.
2. keep the damage the same but give them much better crits. Since ma's are masters at seeking out chinks in an enemy's armor (see their crit buffs) make their weapons do some massive crits so at high levels putting on a tachi with LMA makes sense over fists and shen.
3. raise the damage a bit so they actually increase your average damage, raise the crits a bit, and then allow special MA attacks with weapons that req MA skill only.
Personally I like #2 the best, since it's basically a gamble, I can trade the chance for crits for the consistant damage of MA specials, shen and BwT are like clock work, but with a tachi I could outdamage the special with 2 or 3 crits in the same period of time.