The official packages are always far behind - but that's no bad. Debian does heavily test it's packages to ensure they are as stable as possible.
You can compile Nginx from source to get the newest version (tutorial available on HTF) but you should ask yourself if you really need it.
You won't benefit from automatic updates anymore and it might not be as stable as the one provided by Debian (it actually is, but not in theory
One great thing about 1.3+ (I guess) is SPDY support. There are some other useful modules that are not compiled in by default (e.g. Debian version) - but again, ask yourself if you need them/which you need.
Basically there is no urgent reason to have latest version if you don't miss and features.