I can see the dual set up working well, though am not sure why bother with the plate at all then. I am surprised you have a plate that works in lower temps. I was thinking the plate, since it works through contact or near contact would have to be too hot to touch to make up for cold air temperatures?This depends on the specific plate, some of which do better in cooler temps than others.
I have the Producer's Pride plate and use it alone down to about 50 and then in a dual heat setup down into the 20's (this winter had a cold snap for every hatch I made -- including Easter). The Big Red Bulb keeps the area around the plate warm enough for the plate to work and keeps the water thawed then the plate keeps the chicks warm.
That suits my situation better than a more enclosed brooder with lamp heat only.