I bought the Moon Mirror on Beta, I suspect it was an early version of this offer. It used to show changing moon phases and was VERY cool when active. I bought it for those reasons, but also to find out for myself whether it was an effective supplement to an event.
First off, this building is so cool that many of us begged Inno to let us recharge it periodically. We even offered to pay for the privilege and still they refused. Secondly this building remains so cool, even expired, that I retain it in my city. And the Mirror gets admired by new players, who also want one.
HINT: Even though I think that these buildings have limited effectiveness, I would still buy a new Moon Mirror! I did find that although it gave +1 event litter, it also significantly reduced the incidence of 2 or 3 point litter occurrences, so I have passed on making any purchases since then.