Thank you very much for your kind replies! If you'd like to, I can post some strategies, so we can try to get to 1100 one day.

I have one thing to point out though: one of the key steps for me that tipped me over 1K, was to maximize natural resources. When I quit, I only had 9 oil left. The reasoning behind this, is that heavy industry 1. makes a larger profit than bussiness centra, and 2. are available a stage earlier than the latter one, so they are required to optimize the score for stage 2. The trick is to switch to business centra just at the right point. This yields a lot, but I think that one design philosophy was to make the player aware of natural resource exhaustion. The way I played it, was to continue polluting until it wasn't possible to remain doing so, which is exactly what happens now, and what this game should make us aware of!
So, I propose a score point for every oil resource left, or perhaps 0.5 or 0.2. With a more economical use of oil, it is possible to save 200, or 300. The downside of this idea is that it probably won´t be worth the waiting for futuristic energy supplies (except for fusion). Still, it might be worth considering.