If you are going to do it, I would take ecmilley's advice and have them properly cleaned and flow tested. I don't have much faith in these additives either.
I've had the service done at Rovan Diesel in Mississasuage. Took 'em out, dropped them off and picked them up the next day. They'll provide new o-rings which is a good idea as they tend to get old and crack causing air leaks.
I thought seafoam was a combustion chamber cleaner not injector cleaning product.