Laikipia, Diani and Samburu? Shimba hills?

We have a planned holiday in September with five nights at Laikipia Wilderness Camp and around four nights in Diani probably at Chale Island. Originally we thought of Watamu instead of Diani because of Arabuko Sokoke, Shimba doesn't seem to have quite the same vibe of verdant green and birds. We weren't really thinking of adding another safari destination in due to cost but now are reconsidering if we should maybe add in 2 nights in Samburu probably at Ashnil Samburu, or maybe just spend extra time in Diani and go to Shimba after all. We did think of going to Tsavo (Salt Lick) but figure we might find it disappointing after Laikipia and our previous trip where we went to Meru Ambesoli and Mara conservancies... Help!