The big caveat being the "backup plan" which somewhat implies you are ready and willing to blow up your amps prematurely. Worth it becomes rather subjective. To guys like you and me, yes, but speaking for myself I have a budget of a certain amount of money I plan to spend every year on broken audio equipment. That said, I haven't blown up an amp in a while and I may well change my tune next time I do.
As far as pushing harder, class D amps are most efficient running at max unclipped power (though generally at higher impedance). That's where they get the published efficiency numbers. Running his 4K amp into 1 ohm rising up to 2 or 3 average at max unclipped volume will be far more efficient than running the 2K version at .5 ohm for the same output. Likewise running his 4K amp at .5 ohm to only use half of it's power puts it in a less efficient state even at half power you are still creating more heat. Again, every halving of impedance quadruples heat in the semiconductors.
Lastly we're not talking about running a 40.1 or Crossfire 4K, we're talking about Orion. I would not run .5 on that tier amp outside of burps.