I think it makes sense to have an evaluation - no matter whether he qualifies for services, it will be a good learning experience about where he is in speech development, and hopefully they'll give you good advice about how to proceed.
The way you described it, I wonder if he might have low muscle tone or some other annunciation issue? Anabel (2 years) is low tone, and gets speech therapy that at this point is mostly focused on building mouth and jaw strength so she can pronounce things in such a way that people can understand her. The Mindy - Ninny thing made me think of that; I'm no expert, but I think with some kids the muscle work needed to pronounce single syllables (e.g. Min or Dee) is just easier then the complicated muscle work needed to put them together. For example, Anabel can say many of her friends' names perfectly "Hannah, Ella, Izzy." But she calls herself "A-bel." It's like she just can't get her tongue to do that complicated 3-part A-na-bel motion.
Good luck!