That's a tough one for me. I'm getting close to the soul wall, so the long-term upside of that is fairly limited, and I'm a bit completionist, so I wouldn't mind taking a reasonable shot at all of the upcoming mythics. The big unknown is the crafting system, which might both knock down the "soul wall" (if souls are required for crafting) and/or make collecting my missing mythics a realistic possibility (decreasing the need for maintaining my hoard). For now, I'll probably stop at one if I'm lucky enough to even get that. Gems will always be useful for something, and multiple copies of Pharos might not.