All the AG guys that we put forth into the world didn't build time outside of AG.
I know some of the more, well, austere type of dusting wants a IFR and sometimes also a CFI, I think the SEAT jobs want it too, but most all of the normal AG guys I've come across don't have their instrument, heck many AG planes don't even have a AI.
If you have the extra cash and time I'd get your instrument, but I wouldn't be in a huge rush initially as a greenhorn, most all the jobs which want IFR tend to be higher time jobs too.