Color change - What sometimes works for me whether I'm 10% or 90% into a park and feeling stuck is a Color change. My last park "Function Form" I had big issues completing, It went from being bright and cheery colors to dark and dreary to what it is now - Neutral. Although it ended up Neutral in color every color change I did inspired me to finish another section.

Also, texture change on wall components helps a lot too. If you don't like the windows with the city or factory look simply sink a skylight wedge into them.