The Michelson-Morley experiment was trying to detect wind from the earth passing through aether--the fluid that conducts light waves. It failed to notice any, and is considered proof that there is no aether.
your perceptions of time and distance will conspire to give the same result.
I recently read a philosopher's quote, that I'll paraphrase: A theory which claims to be unmeasurable is probably best left unspoken as well.
Walter Ritz proposed Emitter Theory that suggested light speed was added to local motion, but that was not observed in binary stars as they orbited each other. The example given is that light from the approaching orbit would appear to be C+orbital speed, and therefore the light would overtake previous light, and our observation would be...strange. (maybe reversed)