There are some great suggestions in this thread!

I really like the idea of expansion packs...maybe a new
house (fixer upper of course).

How about a pawn shop...for in the beginning when times
get lean (ex return it for 25% of purchase price?)

Higher priced upgrades? Car, Boat, Vacation...New couches!!
Acquiring all the house upgrades seemed to happen quickly.

Pet food & have to feed the pet or he/she runs away (maybe
pay a fee to get them out of the pound?)

More pet choices (bird cage, hamster in ball, etc) and you
should be able to have more than one.