If you are looking for something to invest in for your tank I would definately suggest liverock at this point. Although it looks like you have a nice amount already the more the better. More liverock will provide you with more places to mount your corals, more hiding and interest for your fish and invert inhabitants, and it will make your system even more stable. I think personally about 2lbs/gallon of Fiji rock is a good goal to start with although If I could fit 3lbs/gallon I would.