To me, the empirical evidence in support of the existence of qualia is so clear and so immediate that I can't figure out what you're not seeing so that I can point to it.

I ... don't think there's much empirical support for the actual existence of the painfulness of pain. Sure, humans experience pain in very similar ways, and you can lump all those experiences into the category pain, and talk about what characteristics are present in all the category members, but those common characteristics aren't a physical object somewhere called painfulness.

As for how this bears on Bostrom's simulation argument: I'm not familiarized with it properly, but how much of its force does it lose by not being able to appeal to consciousness-based reference classes and the like? I can't see how that would make simulations impossible; nearest I can guess is that it harms his conclusion that we are probably in a simulation?

That can be repaired in other ways; given that time travels in one direction for us, our experiences have one chance to be in the real universe, and n chances to be in simulated universes - where n is the total computational power that ever will be directed at simulating historical moments, over the computational cost of simulating a historical moment multiplied by the number of moments at least as interesting as this one. Even if you assign a low probability to the future containing computational power (ie we nuke ourselves before Matroishka shells or Jupiter brains are completed or something), that low chance times n is still large relative to 1. So our prior for being in a simulation should still be high.