Freebitco offers many bonuses. 1. Golden tickets, 2. weekly lottery tickets, 3. Daily jackpot, 4. monthly contest. It's really impossible to determine the effect of each of them on wagering volume.
There are many websites conducting contests and have thread on the forum. Visit their thread and ask them the money wagered due to their contest. Be sure none of them answer, because that's impossible.
If the money wagered due to golden tickets matters you very much I suggest you to check the number of weekly lottery tickets before existence of golden tickets and compare it with number of tickets during the past 6 months.
In my opinion freebitco has a large wagering volume whether there is a Lambo or not. I am sure there are very very few people wagering for Lambo.
I absolutely agree with you. I personally don't think that people were wagering for the sake of the Golden Tickets. I think they were just wagering, you know, as usual, and the tickets they were receiving along the way, were just a good bonus for them.
It is pretty likely that the user who won Lambo, got all his/her 185 tickets from wagering. (Can that be checked, btw?) I mean, one could wager 0.925 BTC, even not paying attention to how many tickets they got for that. And then, BOOM!, "I won a Lambo! OMG!!!"
Has the winner claimed his prize already? Was it Lambo or money?