As someone who has always wanted to own a quality velvet Elvis painting, my observation is that even the best of the velvet painters have not exploited the medium for all of its potential. There is no intrinsic reason (that I can think of) that a velvet Elvis painting could not be as enigmatic, meaningful, or classic as the Mona Lisa.
I know that while there is only one Mona Lisa there are thousands of velvet Elvis paintings. However, one would also have to acknowledge that there are thousands of oil paint medium portraits of women - but only one Mona Lisa.
I think it is more the perception of the viewer that they automatically categorize something (or make a value judgement) that a work is not as worthy of serious consideration ONLY because of its chosen execution medium (velvet painting), and its subject - a million times exploited pop icon visage.
Andy Warhol made the banal meaningful - is it not possible for someone to make a velvet Elvis painting that is in every way equal to the Mona Lisa? If not - why not?