Completing a themed event (5 difficulty levels to chose from) will give you red tickets that can be used to purchase and upgrade theme decorations (found in the Special Decorations section of the construction menu).  Completing a level 1 event will give you enough tickets to purchase the current theme decoration and upgrade it to level 2 for +60 happiness, the same as 2 clothes lines, but for much cheaper.  From here you can upgrade them all the way to +110 happiness.  If you are right on the edge of a difficultly level, remember you are further ahead to complete one, fail one on level 4 then to complete two on level 3.  The other thing is that as you increase your happiness by upgrading your decorations, you may be able to store some and add buildings, so try to leave 2 decorations at level 2 (+60) and focus on upgrading the others to a higher level.  That way you aren't boxing up a +81 when it is time for your third almond.