Bob, closed cell spray foam has twice the R-value per inch, provides significant sealing and vapor control (which I want for conditioned space) and also adds stiffness to the structure. There absolutely are some sound benefits to open cell over closed, especially if it's scraped flush with framing, but I'm doing other sound mitigation work already. The plan is for 2" on the walls and gables and 3" on the underside of the roof as that provides adequate R-value for our climate, especially with it cutting off air infiltration in a big way. For a post frame structure, the additional stiffness it adds to the metal cladding makes for a quieter building, especially when it's windy. Open cell foam really isn't popular in this area from what I've been able to see.
As an asides, the 2200 square foot home addition at our previous property (bigger than our current house!) was done entirely with closed cell foam and the performance was outstanding. And for that stick built structure, it meant walls could be lower cost 2x4 other than those that needed the extra depth of 2x6 for certain kinds of infrastructure.
--
The most expensive tool is the one you buy "cheaply" and often...