Now, this lotto started back in may right? So why don't you go back to a year ago before that, last years may and look at monthly wagered numbers for the whole year before the lambo thing started, that way you get the sense of an average how much was played. Now after that you can check monthly on how much it was wagered during the lambo deal as well.
So, now we have one thing which is 1 year before lambo and you see if there is a % increase every month or so, that would mean that even if there was an increase you would remove the previous increases from this one as well because it was increasing even without lambo and now that increase doesn't count into lambo.
You can also take a look at betting part and how much there was betted and remove those as well considering maybe none of them are related to lambo. So, you are left with whatever is on top of that as lambo increase if you ask me.
Does it really matter the percentage of the gamblers that would gamble if there was no Lambo ticket. In freebitco, There is a provably fair game in Freebitco and everything is clear. No one can cheat you and no one force you to gamble in Freebitco.
Lambo lottery is a kind of promotion. What's the problem? You can win tickets and you can wager to get them. You can also ignore them and leave Freebitco. No one force people to gamble or buy the tickets.