I've fully finished the campaign and all the side missions available (3 government missions and 5 civil). Now, I've bought a medium air ambulance, expecting that it would open up more side missions for me. It seems I'm wrong. I fully upgraded it with every exterior upgrade and I still don't have any extra side missions. None of the available side mission require an air ambulance, nor upgrades such as FLIR or the search light. Even worse, when I play one of the side missions, the helicopter model isn't even an air ambulance model! Only when it's in the garage is it an air ambulance model, seemingly changing it's model to suit whatever mission I'm playing. I didn't even keep the air ambulance paint scheme until I purchased the paint scheme for it!
So, has something gone horribly wrong, or is there absolutely no reason to buy the medium air ambulance, medium luxury, heavy luxury, training helicopter and upgrades such as search lights, FLIR and the tactical benches on the light? I assumed that more side missions would be made available as you progressed, since it seems completely pointless to even bother putting additional helicopter (air ambulance, etc) and upgrades in when they can't even be used. If they're put in just as models to be used in other missions, why have us able to buy them in the campaign? It just really seems like helicopter-specific side missions should be opened up once these new helicopters/upgrades are purchased.