Just throwin this out there as I'm pretty new to the game. If people don't have a reason to attack then they won't unless they just do it for fun. If you don't have resources for them to take when they attack you then there's no reason for them to do it unless out of spite, Like just because they want something to do. but i guess that's the game. You can have super high points, but unless your hurting someone's ego who just has to have higher points then you why would they waste time attacking you? seeing as if you spent your resources on upgrading or expansion
I think wether you expand or upgrade you'll be spending your resources so you won't have any for people to take that have higher points then you. I personally think expanding so you have the availabilty to upgrade when the time is right is the way to go. Build your empire out until your ready to take over.
From several of the post i've read from you, you seem like you know what your doing, and have a great concept on the game. I'm sure you'll be running things around here in no time either way you go with it.
but i'm just a newb, what do i know?