I had an ICF house in South Dakota, and my experience was similar to gnpenning's for energy efficiency. Problem is, for a 4200 sf house and 1200 sf shop, the premium paid for ICF construction was about $80,000 once all was said and done. A well built stick built building will use about 25% more energy; and won't be quite as comfortable. But, you will never make up $80,000 in initial construction costs.
I am building a new house at the moment, and am doing frame. It is sealed airtight; insulated in the wall cavities with high density, high R value insulation, and has exterior foam insulation under the siding. I expect the energy performance to be similar to ICF; it will not be as durable. I estimate the difference in cost would have been $50,000 or maybe a bit more to build it ICF. With $800 a year heat bills going to maybe $600, it would definitely not be worth it. The property taxes on the extra square footage to get the same net square footage might add up to that much. So, ICF would be an expensive luxury, not cost effective.
I had an ICF house in Southern Utah, and it had considerable heat gain on the south and west walls by the end of the day. I did not see that gain in South Dakota, even when the temperature was 100 degrees. A big part of that is the difference in solar input, more than the air temperature, in my opinion.
I like ICF, and feel it is a great material. But, it is a premium material, and has its disadvantages, and its costs. In my opinion, it is not worth the additional costs and disadvantages for a shop in a warm climate. If you want the best and can afford it, price it out and lay it out on your lot and see how it works for you. You will be the one that ultimately has to decide if it is worth it.