Good advice Joe. That said, personal experience for me shows that coins struck on foreign host planchets are definitely ones I tend to send in for grading/certification (if, and that is a big IF, they are mint state). But, I do my homework first. There is definitely value added to off-metal errors by slabbing if the label states the country of the host planchet. For example "Canada 1c struck on Dominican Republic 10 Centavos planchet" or Canada $1 struck on New Zealand 50c planchet" will always fetch a stronger price than the exact same coin with a generic label of "struck on foreign planchet". However, I digress, doing your homework is the "value added knowledge" here that certainly more than covers the cost of the certification, not the mere act of slabbing itself.
Been there, done that, and definitely asked that, got feedback, wise cracks, so I went to educate myself and now I'm back. Still with questions but not the kind that irritate the ole experts!