You sound like me with my old 155. I can tell you from experience, blue backgrounds suck! Literally. They give no "pop" to your corals and make everything just look drab.
As far as rock work, Slice gave you a good idea. What I've found to work best for fish, flow and allowing cool spots for coral placement is adding more branch pieces in the middle and bottom layers. So many tanks have all their branch pieces up top. In my 180, I started with three pyramids. Each one had a cave. Then I bridged pieces across to connect each pyramid, which also created more caves.
Personally, I think you just need more interesting branch and shelve pieces of rock. I don't think your tank looks bad, but I understand the frustration, and if you're not happy with it, it's time for a makeover.