I don't know where you getting appeasimg an existing customer base... And yes, Apple is going for additional market. That is what I said.
Do you really think Apple put any effort on this iPhone SE? Apple is bascially reusing 4 years old design, 4 years old screen for God's sake. Nothing is new for this phone, it is bascially a iPhone 5S casing and screen with iPhone 6S components minus 3D Touch... What smart is that Apple can do this relative cheaply and quickly. There is no production challenges and it can produce tons of this phone in relatively short period of time.
iPhone SE will only be appealing for Apple fans that looking for smaller screen.. Seriously take look at competitive landscape, you have lots of better choice than iPhone SE for same price.
For me, iPhone SE is just Apple's lazy way to response 4 inch market. Apple did not even bother to do a new design.