I like to focus more on the events (I am bad at thinking on content for the actual levels).
Valentines Day- I really think this event should not rely on community prizes. The wheel is also out of the question (providing EA learned their lesson from that fiasco). It will require players to send greeting cards to neighbors. It also bring back everything from last year for new players as well as some new ones.
Saint Patricks Day - This one will not require you to drop anything into your friends towns. It will also bring back everything from the previous year (Leprechaun with well, Pub, and all decorations) as well as some new ones.
Whacking Day - This may or may not happen. I sure hope is does NOT happen personally (even if I missed it the first time).
Independence Day - I think it would be interesting if they added more Presidents as characters (Washington, Nixon, Bush) I missed the event last year but Lincoln would've been a pretty neat addition to my town. They can also bring back some items from the previous event like the Diner and Lincoln's Cabin (obviously).
EDIT: I really hate it when they censor abbreviated words