Airport Express is not seen by Macbook, is seen by iOS devices
The Airpoat Express seems to respond best if its settings are completely cleared first.

To do this, on both the older and newer model, you have to insert something in the one of the two tiny dots which is a hole, and press down in there WITH the unit unpowered, continuing to press while sliding the AE into its little base and for a few moments after. 

This is most easily accomplished by having the AE in the base ready to move into place - then perform the pressing and connecting. I don't need to add, this is a total PITA, but it gives you an AE looking for settings--which you promptly input into AU. 

There is a supposed Reset done by pressing while in place and powered, but it tends to accomplish nothing.