Hmm. I'm going to add a third view to this "restriction for creativity" discussion.
There is something to be said for making the end-game harder in order to make it work to get there, and make the mid-game more restrictive to encourage creativity. That is certainly one way to encourage a smarter building. I think there's another way to do that, though: make everything
easier. In my pack (Colony, link in sig), I've gone through and made a ton of stuff
easier to build, with the idea that if the complicated, interesting stuff is cheaper, more people will use it, as the reward is greater with less expense. So far, it's going alright; with my Galacticraft tweaks, for example, going to and building on the moon has become a reality. I've never gotten to the moon with default GC because everything is such a pain in the butt to get. Now, though, on a server I've played on, there's a fully-fledged moon base complete with Quantum-Tunnel-y thing from AE2, oxygen supplies, and a beautiful base built out of Chisel blocks. If everything had bee harder or even at default difficulty, I would've gotten bored and played something else.
One other thing: there really isn't a way to make people get creative with their builds without also making them stop playing. As such, I suggest you try playing in creative mode with a friend or two and having a small competition: decide on a task to automate - crafting florbs, perhaps - and then see who can get the most efficient/minimal form/outlandishly complex build (florbs, as it turns out, are
really interesting to automate). I did that, and it was a lot of fun.
