for whomever said I had insufficient light: this is sitting right next to a standard cattleya, which is just flowering for the first time. when I purchased both, I was led to believe that oncidiums need less light to bloom than catts, but can tolerate a wide range.
so I think that my previous conclusion about the old one being a dud stands. luckily the new one is blooming up a storm--the buds on spike 3 are really starting to swell!