I prefer luck-based items behind catsacks rather than enforce levelling just to get items.
Newer players may get the items many desire 2 hours in, which in my opinion is a better way to go about as then everyone is on a similar playing field and doesn't feel burdened to play hours upon hours just to reach to a milestone, and then upon reaching that point. Where to then?
Putting things behind units is good because then the player can make their own milestones to get items to build their plaza and bragging rights.
A levelling system in TU wouldn't really work in my opinion, it's a social game after all.
And personally I don't want to see [IDLEBOT #35] sat in plaza just unlocking things by leaving his computer on over-night.
And yes there is a playtime generator for rewarding players for playing '? amount of time' so in a way people who don't gamble or grind still have a chance to get things they desire, which is perfect.