The numbers are in. I thought I'd take this time to do some comparative historical data. Please remember that this data is entirely based on an algorithm and therefore is SPECULATIVE. It is important to not take the numbers at face value and to instead use them as comparisons between one another.

>1st anni (Wakamo)
$1.73m
>1.5 anni (sHoshino/Hyakki)
$3.34m (93.2% increase over previous anni)
>2nd anniversary (Mika/Megu/Kanna)
$9.80m (193.7% increase over previous anni)
>2.5 anniversary (sHanako/sUi/sHinata)
$17.22m (75.6% increase over previous anni)
>3rd anniversary (dHina/Makoto/dAko)
$16.37m (-4.9% decrease over previous anni)
>3.5 anniversary (sHoshino/Kuroko/sSaori/sHiyori)
$12.93m (-21.1% decrease over previous anni)
>4th anniversary (Rio/jkNeru/Seia/jkAsuna)
$10.98m (-15% decrease over previous anni)
>4.5 anniversary (sMika/sNagisa/sSeia/sHasumi)
$10.46m (-4.8% decrease over previous anni)

As you can see, there is a general decrease in revenue after the 2.5 anniversary. The biggest % drop being between the 3rd anniversary and the 3.5 anniversary - the anime and the numerous dead months took their toll.

However, this data does not exist in a vacuum. Optimally we would have player count for normalization. Our best data for this is raid participation, for which we have adequate historical data thanks to Twitter autists.

>1st
180k players spending $9.60 PP
>1.5
270k players spending $12.37 PP (28.8% increase)
>2nd
370k players spending $26.49 PP (114.2% increase)
>2.5
529k players spending $32.54 PP (22.8% increase)
>3rd
685k players spending $23.91 PP (26.5% decrease)
>3.5 anniversary
626k players spending $20.65 PP (13.6% decrease)
>4th anniversary
576k players spending $19.07 PP (7.6% decrease)
>4.5 anniversary
525k players spending $19.92 PP (4.5% increase)

For the latest anniversary, there was a slight rebound in purchasing power. Again, this is just estimates based on the data we have.