I think Messi was never as close with any player that left us before as he's with Suarez now. Sure, he had good relationship with many of them. His first friend was Ronaldinho but that was more of a mentorship role and he was basically still a kid with nowhere near as much power than he has now inside the club when Pep decided Ronnie must leave. He had great understanding with Alves on the field but I don't think they were as close off the field because they are just different characters. His relationship with Cesc was probably the closest to what he has now with Suarez and Cesc left on his own will, so Messi was understanding that. I don't think he would have any problems if Suarez would decide to leave to China or go back to Uruguay in 3-4 years but he could be thinking about leaving if he'd thought that the board wouldn't want to keep Suarez.
Agree about high wages in general but I have no problems paying top players. It's bigger problem when you overpay for someone like Song who you mentioned. When Messi will sign a new contract until 2021-22 we'll also be aware that he probably won't deserved to be paid 35 or 40M per year at the end of his contract when he'll be 35 and will most likely decline. But what else can we do if we want to keep him? Same with Suarez. We are paying him for what he can deliver now and over the next let's say 2 seasons, then it could become troubling if he won't perform on top level anymore. It's not ideal but if you want to keep great players you have to pay them. We should absolutely improve our paying scale for 2nd, 3rd or 4th range players though if we want to stay financially stable, especially when we'll start renewing Camp Nou as well. But once you start to pay fringe players high salaries it's hard to get back because players that are brought in (or better said their agents) in most cases know how much other players in their positions before them were paid. So why would they accept less if they think they are better than players they are replacing? Of course that's not always true but they can use that argument during negotiations.