Have you actually tested and seen perf differences that are significant enough to back up what you're saying?

Yes...your concession earlier that performance on these server-based tasks will be better <s>

I think we're running with different crowds - I know a number of database developers (and database developers in the making) who are running server-based environments on a single desktop.

The world of BI is such that many have to know everything from ETL to OLAP modeling to report deployment to creating dashboards (and even using .NET with MOSS or PPS). You need a server environment for this type of testing/developing/experimenting to do this, which you've already conceded will benefit from 64-bit.