Board Thread:General Discussion/@comment-12330013-20160101022123/@comment-24577221-20160107030642

The "Save Up" achievement is supposed to be for earning whatever-number of coins, not for having that amount at present. That is, if you've forked out lots of coins to buy the expensive structures, that shouldn't count against getting the achievement. Or so I infer from the description, which specifies "earn" rather than "save".