Seems to me the odds of hitting the 500 get $500 is pretty tiny. I believe it includes every player in the entire country who has ever had a B Connected Card. If it was limited to people who have ever set foot in the casino, it might help a little.
I thought the cows and trout games were tied to tier level too. I almost always get 10,000 points and I have heard other players complain they always get the minimum amount. The only time I remember noticing a decrease in my swipe was when I had not given them my usual level of play for a month or so. I have an Emerald Card but the couple of times I have swiped at Sam's Town, I got the minimum swipe amount, probably because I have hardly played there in the last couple of years. If I had to guess, I would say the top amounts are probably awarded on a random basis, perhaps not related to play level.