I've been playing the game actively since release, and have never put any money into the game. The thing is, up until a few months ago, there was no reason to spend money. Everything you could buy in-game was either available for free through Pokéstops, or could be purchased with coins, which could be earned through the gym system. Unless you're a massively dedicated player who wants raid ten times a day and have nine eggs incubating at once, simply playing the game was enough to get you most of what you needed. Then a couple months ago everything changed when they added an even for Regigigas, which was basically the same thing as this Genesect event. It cost eight dollars, and you could only purchase it with money, not with coins. If it cost 800 coins instead (equivalent to $8), or even 1000 coins, then I would buy the ticket in a heartbeat. But no, you have to pay eight dollars, and I honestly don't think the virtual rewards they give amount to anywhere near eight dollars worth of value. I was really hoping that the Regigas event would be one-time thing, but now they're repeating it with Genesect, much to my disappointment.
Of course, everyone's going to value the game differently. I don't think people buying into the event is wrong, but personally, no matter how much I play this game, I wouldn't have even started playing it in the first place if it costed me eight dollars, and if I wouldn't pay eight dollars for the entire game, there's no way I'm going to pay that for a tiny one-day event.