I have read before that those plates are a waste of money. For a ride plate to do any good it needs to attach to the shoe as well. I would go with a ride plate/shoe before installing the nos. I've read that you need a rideplate/shoe for anything going faster than 70, although you seem to have done fine without it.
Is the intake set back, or can it be set back more than an anch or two? If not may not be worth while? I bet you could gain a few mph with a set back and a shoe/ride plate. If you want to do it yourself I can send you some pics of how I did mine. Jack and Hammerdown really helped me out and I took really good notes.