The proposition is not testable so I can't see how there could be a wager. The evidence is the usual evidence for MWI -- either none or the whole of quantum mechanics, depending on your point of view :-)
But think about it -- if (as the MWI says) every time you face a choice you make all possible choices in different branches, what could you possibly do that would affect the set of all branches?
Think of Tic-Tac-Toe's game-tree; that's a set of all possible choices that can be made in different branches of the game. Once you have an idea of the shape of the results those choices, such as "putting an X here causes me to lose more often than I win", you can make your choice based on that information so that you /don't/ choose the portions of the tree with the worst outcomes, thus narrowing the range of potential futures to ones which are better. Instead of spreading your future probability across 26,830 distinct timelines, in which you win...
I haven't been able to find the source of the idea, but I've recently been reminded of:
This is, of course, based on the Multiple Worlds Interpretation: if the lottery has one-in-a-million odds, then for every million timelines in which you buy a lottery ticket, in one timeline you'll win it. There's a certain amount of friction - it's not a perfect wealth transfer - based on the lottery's odds. But, looked at from this perspective, the question of "should I buy a lottery ticket?" seems like it might be slightly more complicated than "it's a tax on idiots".
But I'm reminded of my current .sig: "Then again, I could be wrong." And even if this is, in fact, a valid viewpoint, it brings up further questions, such as: how can the friction be minimized, and the efficiency of the transfer be maximized? Does deliberately introducing randomness at any point in the process ensure that at least some of your MWI-selves gain a benefit, as opposed to buying a ticket after the numbers have been chosen but before they've been revealed?
How interesting can this idea be made to be?