meh
too much work.
11k presents at the current market price means more then 2 mil coins. With 2 mil coins I can buy a lot of rainbows and use them once at every 4 days, without getting headaches to be on and keep an eye on the darn buff at every 12 hours. I have problems to keep the epic workyards buffed (soups, 12-13 hours dropped by friends/guildies, that's why i can compare), i keep forgetting to buff them, so, high chances that i will forget the market too.
Plus the logistic to reorganize parts of my island for efficiency... more costs, moving lvl 6 buildings is not cheap.
Oh, and it may looks cheap to use it, but 500 gold bars at every 12 hours means the gold smelters have to work, and that means the gold mines have to work...and buff them, of course. And more coal consumption too, which, with forge in the picture, is not something to disregard.
All for a 12 hours buff? meh