I first agree the EPD is actually fairly well diversified, however, a group of MLPs certainly makes sense and does offer additional protection to stabilize a return. As was already stated TurboTax does my 10 MLPs just fine.
You mention diversifying to get a higher yield. A couple thoughts here. First is Factoids CAGR. Howfast is the distribution growing. Does no good to buy a MLP with a 2% higher yield if they do not grow their distribution, does it? A slower steady grower might in the longer term provide better growth.
Second is that distribution yields generally equate a balance between future growth and risk. Those MLPs with higher yields are either perceived as having less growth potential, have a riskier business, or are weaker financially. Thus the E & P sector has high yields due to risk and some of the smaller MLPs higher ones due to lack of financial strength.
EPD is my core holding and the one I bought first. Adding additional MLPs now might be a good plan.