Alright, let's see where to start with.
realkman666: Is Tropico 3 close enough?
No, it's not. Tropico series is awesome, love them, but you will easily see for yourself that it's not a city building/management game per se. It's a really good game (though the 4 is better if you ask me), but not what you are looking for.
realkman666: does SimCity 4 still hold up visually?
This is completely biased, but I would say that: Hell yes is is.
It's pre-renderized 3D building looks as shiny as back in 2004. However, it won't be as satisfying as looking and moving your camera around your city, something you can do on Cities: Skylines.
On SimCity 4 defense I may say that Cities: Skylines looks a bit cartoony, like SimCity (5).
realkman666: Is Cities: Skylines so much sleeker that I should just wait for it here??
I doubt it will come here, so my best advice is to eat your pride and get in on Steam or to just stop torturing yourself trying to compare a game all city building simulators lovers are praising all over the internet as the replacement for SimCity 4 with the already mentioned.
I'll say something I expect doesn't hurt anyone feelings, but it's a truth no one can deny:
We'll all die. Sooner or later, but we will die. No matter what are your believes about afterlife, I doubt you will be able to play Cities: Skylines wherever you think you'll go.
So, will you play it, have fun with it and forget about using a DRM system you hate or will you deny yourself the possibility of playing it because of that hoping that it may come to GOG in an unknown future?
I hate DRM, I will always prefer GOG versions, BUT I will probably buy this once it goes on sale.
The reason?
I want to play it. Simply as that.
No reason to forbid myself doing something that I want and is completely legal.