I've actually done just this and gotten elemental or stat materia several times, so although it might seem to increase your odds, it isn't an absolute method of prevention for getting those types.
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^ Yeah but if I am correct, if you put in an INT V, it can't become an Int V, so instead of using 5 of the same materia, spread them out with the most worthless ones.
The problem is not the money. Gil are very easy to make. I have enough to buy 2 large houses and decorate them. The problem is there are not enough plots. Even after 4.2 there will still be people without one despite having the gils.
Yeah shifty making with master mutamix rarely gives the materia you want.
Assuming the chances of getting each materia from Mutamix are even and all of the materia you're using are of different types (I personally use dexterity, mind, intelligence, piety, and skill speed if I'm burning clusters on this), you'd have about a 46% chance of getting a DoL/H materia that's generally worth more then all five materia put together.
It's still likely going to be too much of a gamble to be very profitable, though.