What, pray tell, are those 'demonstrable benefits'? You can only use the subset of XHTML 1.0 described in Appendix C, which means you cannot use any features that XHTML offers over HTML. Besides, AFAIK Gecko browsers don't support incremental rendering of XML documents, which may cause poorer perceived response time.
The presentational markup is already deprecated, and has been for over 10 years. Browsers still support it, since they must be able to render 10-year-old documents, but it's deprecated nevertheless.
What really separates Strict from Transitional is the mindset. A Strict DTD emphasises and promotes better separation between content and presentation, which has major benefits for accessibility and maintenance.