Monster Z 1.2 speaker cables....

For a budget system...would these be a marked improvement over original monster or similar cables?
Never heard the M series cables. It might be an improvement over the original cable, but knowing Monster, they probably are inferior to their competitors.

For a budget system, try Belden or Canare sold by Blue Jeans Cable.

The Belden 5000 series 10 gauge is a great "Bang for your buck." They provide neutral, uncoloured sonics and are used by many Agon members. I have a couple of their interconnects and they are as good as some high-priced cables.
If your talking about the M 1.2S cables, don't think you'll hear much difference. Check out Atlas Equator 2's. Superb spk. cables. Very pure copper. I'm extremely impressed by these cables and I completely have no desire to upgrade.