Something Blizzard is doing to help find that balance is a new system, Nephalem Valor, which he pointed out is “still in testing”.  While the developers are still “working out the details” of the end game Valor system, Bashiok did share how it “currently” works in Diablo 3.

Kicking in at level 60, the Nephalem Valor buff is granted when killing a Rare or Champion pack.  While Rare and Champion packs still drop loot, they buff they give you grants increased magic find and gold find.

However, if you change a skill, skill rune, passive, or leave the game, the buff disappears.  As an extra reward, if you kill a boss while this buff is active, you’ll receive extra loot drops from that boss.

“The exact amount of magic find and gold find provided by the buff is still being reviewed, as is the amount of extra loot you get from a boss while the buff is active,” he said.  “We’re also playing around with whether or not the buff stacks, what the duration should be, and whether or not it should persist through death. We want to make sure the buff is strong enough to make staying in your current game more rewarding than creating a new game. At the same time, if the buff is too strong, it risks making shorter play sessions feel not worthwhile.”

“We expect this system will encourage players to stick with a skill build of their choice, select an area of the game they enjoy, and sweep it for rare and champion packs on their way to a boss, finishing off a run with a boss that’ll be worth killing. If you wanted a shorter play session you could be done at that point, but if you have more time, the path of least resistance would ideally be to stay in the same game and make your way towards the next boss.”