Well, not necessarily. If a pair of Sun Exxx's in a cluster was cheaper, faster and more reliable than a rack or two's worth of 1U Dells then it would be a no-brainer.
Right now, for most applications, AMD64 beats SPARC. I would love to run Solaris on AMD in production. I can't tho' because Solaris x86 doesn't get tier-1 support from a couple of vendors I rely on. The choices are SPARC/Solaris or Intel/Redhat, and despite the fact that Red Hat is a complete pain in the arse, I can't justify SPARC/Solaris on grounds of better manageability and I can't do AMD/Solaris either. That is where Sun could make some quick wins.
No - this is where I think the worlds collide. You're basically saying they should commoditize their own hardware to the point where its at parity with Intel. I'm saying they need to do the opposite - they need to increase (or at least maintain) their margins and focus on selling it to the people who really need it - enterprises and top end institutions that value the incredible robustness and scalability you can only get with that kind of hardware. I think trying to do both ends of the spectrum on the same platform is just going to ensure they do neither effectively.