XPath 2.0 and XSLT 2.0 are larger and more complex than their predecessors. Schema support and “strong” typing will catch errors, but they will also force more explicit casting.
Does it make sense to start developing for 2.0?
Yes, I think so. Grouping, regular expressions, user-defined functions, character maps, standardized access to result documents and multiple result documents are all going to make stylesheet writing easier.