2. Is the environmental impact of the computing power required to generate vanity addresses justified for personalization purposes?
The energy required to generate a vanity address is in the same order of magnitude as using air conditioner or electric heater for a few hours.
No crypto activity, not even Bitcoin mining, is a significant contributor to global warming. Bitcoin network might consume a lot of electricity, but it's still a small fraction of global electricity, and electricity itself is a small fraction of global greenhouse emissions.