I haven't heard that they were any noiser than other HDDs. It seems lilely that they would be, given the higher spindle speed, but this would be mitigated using some of the anti-noise mounts inside the case.
Questions is - will you really notice the speed difference ? I can't answer that for you. It's a balancing act between speed, noise and cost. I'd try googling some reviews on velociraptors and seeing what they say on these points. However I agree with Ars on this.
"The problem is that SSDs or even VRs are still a substantial chunk of the budget, and while they're nice, the extra money is probably better spent on a faster video card.
"
Of course
YMMV.