Wow, plenums. They were sort of on the tail-end of being in vogue when I got into the hobby about 10 years ago - people either had a plenum or a bare-bottom tank. It seems to me their usage sort of peaked in the mid-90's. I ran my first reef system on a plenum and it seemed to work out OK except for the 2 years or thereabouts that I had a jawfish who burrowed down to the plenum and rendered it ineffective. But when he wasn't in the picture that was a clean reef tank.
Anyhow it seems to me people realized that you could run a DSB instead of a plenum and have just as nice a system and then people realized you could run a shallow sandbed instead of a DSB and have just as nice a system and then people realized you could have BB tank instead of sand and have just as nice a system and that basically would take us full circle if it wasn't for that plenums don't seem to have made a huge comeback.
Anyhow I guess the point being is they are just another way to run a tank, there are others, the only thing that makes it wrong or right is how happy you are with the method you choose.
Oh to answer your question about the front panel, what I did was have the plenum have a sidewall and push it back from front glass so that I could fill the gap with sand. So it looked like a DSB instead of a plenum.
I wasn't unhappy with the method per se but I myself wouldn't bother going that way again. "Been there, done that" kind of thing.