OK, our general feeling is the Suppressing Fire and Pinning are too powerful as they stand...
My thoughts to fix that without completely scraping and rewriting the rules are simply to make them less powerful.
First, on Suppressing Fire, remove the WP penalty to the Pinning test. Make it a straight WP roll. Comparing Suppressing Fire with other Fear based effects (and while not exactly the same, Pinning and Fear are close kin) being shot at is not "man next to you dies vomiting maggots."
Second, reduce the BS penalty for being Pinned from -20 to -10 and remove the "may only perform Half Actions" clause. This brings being Pinned into line with low level results on the Shock (Table 8-11) table. Leave in the "find/stay in cover or retreat" clause because it makes sense and is characterful.
Another option would be to just make Pinning and Fear the same thing. Suppressing Fire forces the targets to make a Fear test at (+0). If targets fail they need to roll on the Shock table (Table 8-11) which gives a range of effects, some significantly less serious than the current Pinning rules, others much worse depending on exactly how badly you roll. Personally, I'm leary of this idea because I'd prefer my characters not faint dead away during a firefight... but it's an option.
Just my thoughts...