I would keep the PPQ and the Glock. From what I understand, the PPQ and the PPX are close in size size. I am not sure why the PPQ is less likely to be carried. Also, the PPQ supposedly has a better trigger and as you stated, you think it is one of the very best pistols money can buy. I would carry the Glock most of the time and use the PPQ for home defense if I were in this situation. As I understand it, the PPX was created to be more of a budget model and is a lot less expensive than the PPQ, so if you got rid of the PPX and wanted to buy another later, it would be cheaper than doing the same with the PPQ.
However, I have never really seen the need for two guns to fill those two niches. If you bought a Glock 23 or something else of similar dimension and design, it serves both purposes well, you could sell the other three pistols and spend all the money on ammo or reloading equipment!