The best use of your Ninjas III PlayMesh Points is going to be on Ninjas III Clan Members. The reason for this is that Ninjas III Clan Members get gradually more expensive the more you purchase. You have to purchase these both because a single Clan Member can only control three pieces of property, so you have to keep purchasing them so that you can continue investing. As the price goes up you are going to find that the primary expense that you have is on Ninjas III Clan Members. You should use the majority of your Ninjas III PlayMesh Points, then, on Ninjas III Clan Members.
When you are buying Ninjas III Clan Members the normal way, try to not buy too many at one time. The most important place you put your money is in real estate, but Clan Members are required for real estate. With this in mind you want to buy as many pieces of real estate as you can without purchasing more Ninjas III Clan Members, then buy more when you are told to. This is the best balance and lets you put your available money into real estate.