Pardon my ignorance. But why not just upgrade your Sport to Private? I'm from Canada so I don't know exactly all your rules but I would imagine you would have something like 20 more hours of instruction or something? Then you can flight night VFR and perhaps your insurance would be less. Plus you have your own plane so you can get a freelance instructor for 60ish bucks. What are the plus sides in the USA for staying as a sport pilot?