I've thought about that too. My family thinks I'm nuts, but I'd rather win the "small" prize. The big one is just too public, too much responsibility...too life-changing. I talk about what I'd do with it, but actually being in that position would be very stressful in a way.
I am so not into drama!
I'm going to say $800,000 (after taxes) would be enough for me to move (read, build my dream house) so I guess that's the life-changing level. Below that, I'd probably put it toward less dramatic things - pay off debts, DS's college tuition, trips, improvements to our current house, extra in the retirement savings...mostly things that would happen anyway, but faster and better.
I said $500,000 because I think we could get the house and land we want for that. We have enough equity in our current house to pay it off and misc debt (a car, student loans, etc). So if we then kept working and had no student loan payment, mortgage, or car payment...that would allow us to travel more and save for a better retirement and save more for kids college. Having that assurance would be "life changing" for me. Now, we will probably get there anyhow, but it would be nice.
Anything between say $1-$4 million and we would be in the gray area of it being a ton of money, so much that we may have to quit our jobs, but not so much that it would replace healthcare, salary, other benefits, etc. for the rest of our lives (we are still in our 30s), especially if it got mismanaged or if friends, family, general onlookers decided to sue us or mess with our personal security.