Thanks, your post was very helpful.
The Babaganoush looks very interesting. Though it seems to only support getting product information. At this point I am not seeing any create/update. Also it is something that seems to only work within the sitefinity project itself.
When you say you can 'Another option is to create your own with e.g. WebAPI or ServiceStack.' I am assuming that this is also creating a WebApi layer that resides inside of the Sitefinity project? Ideally I would prefer not to have this limitation. I would prefer to have a project that is not a part of my public website to handle this type of action.
I guess I am used to working with API layers that allow me to reference dlls and then start using them. Unless I am reading things incorrectly it seems that you have to go through your sitefinity project if you want to use their api. If this is the case I find that very disheartening.