I don’t say this to be combative, but I certainly didn’t get that impression from the way you asserted that it’s only a problem when a certain player wants to build in a certain spot, rather than a more general problem with overbuilding and server populations 
It doesn’t have to be “incredibly challenging”, it just has to be enough to make at least a portion of those people start questioning whether it’s really worth doing after a month or so.
@Taemien’s idea with BP challenges is a step in the right direction. Before the BP, I had a suggestion whose gist was basically to add an upkeep system where literally anything you have as a leftover from your normal play could be used as “upkeep fuel”.
Would either of those two ideas get rid of all serial refreshers? Nope. Would it get rid of a certain portion of them? Definitely. Would it be enough to let the servers “breathe more easily”? I don’t know for sure, given that we’re talking about G-Portal, but I would hope so.
Like I said, that motivation isn’t binary, it’s not “either I’m motivated or I’m not”. Some people are willing to do more, some less.
Right now, we have more buildings and less players, and I can’t say it’s for any “right reasons”, really.