I've heard some pretty bad stories about plenums going bad. Note I say HEARD as I've never had a plenum myself. I do have a FUGE and honestly I wouldn't run a tank without one again. The benefits of the FUGE are tremendous and the drawbacks are NONE. In addition to nutrient export you also get the benefit of a budding and growing POD population ( I like to call it a PODpulation) which will also benefit your whole tank. Many Fish LOVE pods and some species dine on PODS exclusively. An added benefit is that the FUGE is really cool to just sit and watch. Many nights I have caught myself looking into the FUGE at the various life forms swimming and playing in there and not the Display Tank. IMHO a FUGE is MUCH more than just an option.... it's PART of the total reef.
Good luck and HAPPY Reefing
Allen