Me personally, I only use one shake a day, one scoop. Sometimes 2 in the off season. But I try to limit it at that.

As far as dropping the Dex level, that's fine if that's what you want to do. But you'll need to add in some other carbs for that meal, and not just drop it to a shake and 40g Dex. If it were me, I'd add in 40g worth of oats (about 3/4 cup dry measure). Something lower on the GI scale. There's a lot of debate over whether pwo carbs should be more high GI or low GI, and I prefer to keep it pretty much in the middle; some of each. But whatever way you choose to do it, you need to keep pwo carbs fairly high.