No worries, all that I have mentioned are merely ideas, actual execution would have to be balanced and thought out before implementation.
This game and minecraft shares many similarities. However, the distinct difference between this game and minecraft is as you have mentioned, the threat of destruction. Games are essentially problems waiting to be solved and in finding a solution, it entertains the player. Minecraft is so wildly successful not merely because it is a voxel block builder - but also because it has that exact same mechanic that causes players to be constantly on edge, which also means there is always something to do. There is never an ‘end’ to minecraft - bases have to be continually secured, progression is constantly threatened with regression if caution is thrown to the wind. This is what keeps players playing - because there is continually something to do, a problem waiting to be solved (nightfall when mobs spawn in minecraft for example).
Minecraft goes one step further with a sandbox mode to appeal to people who have no interest in ‘defending bases’, who just want to build and gain pleasure from accomplishing a build. This game can similarly achieve that with safe buildings in certain worlds, as I have earlier mentioned.
Portal networks provide convenience, however, if such convenience were to come easy, there would be no challenge and without challenge, this game will continue as it is currently, which is actually quite decent, considering it does have about 100 odd players on at any one time…but then again, the purpose of this thread is focused on improvement, not maintaining the status quo, therefore, in order to achieve what one has never achieved before, one must be prepared to do what one has never done before.
Also, with regards to defending constructs on higher tier worlds, we must remember that this is an MMO, with multiple players on at any one time. Defense does not have to be borne alone. This has also the side effect of bringing about more importance to guilds than just mere buffs and promotes team play both within the guild ecosphere and on a greater scale, the entire gameworld as other players who have a stake or who are out for the rewards would similarly help with the defense. Once again, emergent gameplay would result - due to the need for consistent defence, networking will play a greater part in this game, guilds will evolve to have a more varied roster, alliances will be formed, contracts made with smaller guilds for the sole purpose of hiring more ‘guns’ to support incursion defense.
So, yeah, we are in kind of a stalemate.
