How about do thing, get money, spend thing to get decoration(s), decorations give skill points, spend skill points to do thing better, and repeat? Also, if you add achievements, you could get players to play for 30 minutes at a time.
Do you have any decoration ideas? I actually was working on that and ran out of ideas, I have a one of those lucky cat statues. Achievements is actually really good I didn't even think of that. I can just make achievements for all the random stuff I added while procrastinating on the actual gameplay.