Purpose beyond first Jhana? If access concentration, or at most the first jhana, is the requirement for successful insight meditation what is the purpose of the other form and formless jhanas?
Although the higher jhanas are not required, they're strongly encouraged by the Buddha evident in the high frequency with which they are mentioned throughout the suttas. Ven. Gunaratana in his "The Jhanas" wrote: 


  The Buddha is constantly seen in the suttas encouraging his disciples to develop jhana. The four jhanas are invariably included in the complete course of training laid down for disciples. They figure in the training as the discipline of higher consciousness (adhicittasikkha), right concentration (sammasamadhi) of the Noble Eightfold Path, and the faculty and power of concentration (samadhindriya, samadhibala). Though a vehicle of dry insight can be found, indications are that this path is not an easy one, lacking the aid of the powerful serenity available to the practitioner of jhana. The way of the jhana attainer seems by comparison smoother and more pleasurable (A.ii,150-52). The Buddha even refers to the four jhanas figuratively as a kind of Nibbana: he calls them immediately visible Nibbana, factorial Nibbana, Nibbana here and now (A.iv,453-54).