I *will* spend dias to get at least Silver league, as my Elf city needs the Forge to complete the full set.
My Human city spent about 9k dias last year, so it has 2 full sets already...
However, it's still tempting to aim for gold league again, since it would give a 2nd copy of the main Ruins building, which would allow for the option to potentially put out 2 full sets in the future once you hit the Sentient -> Ascended chapters, and probably do away with the T1-3 manus anyways?
Those sets will provide enough T1-3 on their own to fulfill the various "gather 'X' T1-3 goods" quests, and having those various goods producing event buildings out of whack for 7-10 days to start events is far less of an overall headache in the later chapters where T1-3 goods production is basically near-pointless anyways.
With a little luck, hopefully Beta is beginning the next event just before our current one ends and it'll be possible to see whether or not it's worthwhile going for gold league this time, or saving up for what's likely the "Part II" of this current event.