I have bought tickets before, when the prize money gets really large.
I mean, the single biggest increase in chance per ticket purchase is from 0 tickets to 1 ticket, since you go from having 0 chance of winning to 1/47 million or whatever it is.
After that, buying additional lotto tickets is pointless. You need to buy such huge quantities to really affect your chances.
That's not to say I haven't gotten into fights with people, coworkers in lotto pools, etc. "Oh man, if you buy 20 tickets, your 20 times more likely." Well, okay, but if it's 1/47 million per ticket, now its 1/2.35 million, and you're still guaranteed to win nothing.