I'd have to say my lower chest is pretty fully developed and I've never done decline, my whole routine consists of heavy flat, then a few incline exercises
I like doing bent forward cross over cables, with hanldes at the bottom of the machine, the first time i did it was about a year ago, and i felt a burn in my lower pecs like nothing else i've ever done....
I'm not a big fan of declines... just something I never really got into.... But like everybody else is saying.. if it is something that is working for you, why bother messing with it?