I'd go for it. Wal-mart Canada now stocks 16" pizza stones for $9.99. ( a very good deal )
at that price, you can experiment, and it won't cost you much. I have one on the bottom and
one on the top in my oven, and I swear it helps.
The upper one needs to be pretty close to the top of the pizza in order to give any benefit,
and it has to be really hot, or else the opposite effect will be achieved, but in your oven, I bet
it will really work well with the high temp you can get. My oven goes up to about 550 F max.
Get that upper stone hot, and have it no more than a few inches from the top of your pizza,
and I bet you'll get great results. It's the closest thing in terms of imitating a deck style oven ( low ceiling )