In many ways the Intel of todays owes much to that very backstep that the Opteron forced Intel to take.
I'm not sure if we should see that as an advantage. It means we're stuck with the inefficient x86 architecture for many more years.
Had that not happened, it's quite possible we'd still see Intel working on refining the netburst architechture and quite possibly there would be Core 2 duo or Nehalem as we know them today.
Most probably not. Intel's roadmap for x86 ended at Netburst. There was never a 64-bit model on there. The plan was to make Pentium 4 the last x86, and keep the platform 32-bit only. Then migrate to Itanium for 64-bit and get rid of all the legacy that is x86 and its software.
IMO - it was a far larger shake-up of the world of computing in general than the PPro.
Pentium Pro is when x86 stopped being CISC and started being 'RISC'.