It's going to be interesting seeing friend list fragmentation as the game progresses.
At the start, Chizuru was everything. If you had one with her own TM, you were in the upper echelon of friend units. Then Fencer w/ Enhancer was sought-after. Lightning was the big business for a while, then Luneth, then Elza, then, then, then... for the most part, each new physical 5* base more or less replaced the other in desirability. But as Aileen and Tidus and so on roll out, friend unit value is going to change dramatically.
Chizuru and Lightning and Luneth and Gilgamesh were broadly useful regardless of your team setup, since "highest ATK, best friend unit". But if I have Orlandeau and not Aileen and a third of my friends list switches to Aileen when she releases, that doesn't help me in any real way (and vice versa).
When Ramza gets his enhancements, sharing him will be a pretty useful thing to do... but I have one. I don't need a friend unit Ramza. Though a person who pulled two Orlandeaus/Aileens/Tidusii might value one.
130 friend spaces is a lot, but I can eventually see fragmentation reaching the point where you have to start targetting specific friend units more carefully.