Wait... I'm almost certain that +1 decreased MP Consumption only works if you have 10 points of it. It's a set effect, but it's applied by enchants. Look at Attack Speed boost on my Gun Log, if you don't have 10+ points, there's no effect. Since my blunt master wasn't over 6, I only got 8 points and it wouldn't activate unless I wore another piece of gear I had that gave me another 2 Attack Speed points.
My friend has a gear set with Decreased MP Consumption adding up to 10 and it gets applied at that point. However, the upgrade form of that, the 4% consumption decrease on my Hermits Staff, is applied immediately.
I guess we need to be careful about set effects inside of enchants, not just on the item itself. Also you should look at the Karis Set if you want more info on the mp consumption decrease
Edit: Also if nobody said this already, are set effects stackable? Like 10 points of something = 10% and 20 points = 20% of whatever boost?