I'm on Golden Rainbow. If I leave my main country in Secured Mode, is there any point in having Fortifications there? I'm just looking for things I can do to save money.
Golden Rainbow is the peaceful world, so as far as PvP goes, there is no point of you owning any. Saving money is reactive, instead think proactive, do somethings that can boost your income, rather than cutting costs. For example, if you have well-established corporations, they may have a steady 0.5B profit income per month, so it would be okay to increase your corporate profit sharing.
I just reached Game Level 2, and found out I'll probably need more foritifcations to reach level 3. It's a good thing I hadn't started selling the ones I already have. lol
As you found out already, Forts are involved in upping your game level. Aside from that they are obviously only important if you are planning on defending yourself.