I don't think dextrose is of much use to you unless you drop low. However, after a hard workout your non-insulin dependant GLUTs (GLUT2? I forget...I'll look it up if you want) will suck up a good amount of the available blood sugar so you may want a quick acting sugar to keep you from dropping too low...but you know that already. You can spike whenever you want so I don't see a special reason to take extra dextrose, although an acute dextrose dose followed with a quick acting insulin theoretically could shuttle more into your muscle. I say theoretically because, as you know things don't always work the way one would think they would in your state.