This is a very good point. Without the competition from AMD, we'd probably still be waiting for the hardware virtualization and 64bit extensions. I'm pretty sure Intel wanted to use 64bit as an opportunity to move its customers to a more patent-protected architecture. Way to go AMD!
Not sure Sparc has really motivated Intel much...? Every Sparc I've ever used has been large, hot, and slow for real-world workloads. But maybe I'm just scarred from having to lug around a Tadpole for a year.