I'm not saying they should have sold Long $3M. I was just disagreeing with the idea that holding on to players that want to go won't hurt you in signing future younger players. You think Kaku is going to recommend RBNY to players from his former club if he doesn't eventually get his move to Mexico? I wouldn't bet on it.
Also, I 100% believe Kaku's issues were because he didn't want to be here. He was almost an MVP quality player last season with, what seemed like, an amazing attitude. This year, he doesn't get his move then he acts on twitter, he plays poorly, stupid red cards, suspensions for kicking balls in to the stands... He was clearly frustrated with being here. There's a direct correlation between us not selling and his poor play.
Murillo, I don't know because I don't remember a specific offer for him, so I'm not sure if he had his heart set on a move. There was definitely talk of him wanting a move last season and then he takes a MAJOR step backward this season after it doesn't happen. Could also be that he got paid more at RBNY and now cares less.
And, yes Lawrence was fine after he didn't move. Every situation is different. Handling this stuff is an art, not a science. In Lawrence's case we were better not selling. In Murillo's, we would have probably been better letting him. You're analysis is just too simplistic, and doesn't take into account how players will react.
Kaku had a dip in production in the second half of last year where he started off leading MLS in assists and then had no assists at all for quite a long time. He then didn't make Paraguay NT, which meant a lot to him to the point he changed his citizenship from Argentina. The bottom line is, your belief that he struggled because he wanted to leave is a pure speculation, given that he really wanted to make Paraguay NT and already had some struggles last year, so this was not a new phenomena to go through below average spells, and he is back to playing well again. Murillo as you said didn't have an offer that we know of and sucked, while Lawrence did and did't go, yet produced well. So, all in all, there does not seem to be an evidence to suggest plays start to suck when we get a bad offer for them and decide not to move them.
As far as Kaku's friends, I think if the club treated Kaku well otherwise, and we offer his friend good money, he would not be opposed to come here. Think about this, we spent entire last summer negotiating for Kaku, working with agents, and got him for $7 mil transfer fee, plus some other expenses to agents, etc... Then he has a very good season, makes Paraguay NT (I think he actually started there when Liga MX called), and as you just said, was MLS MVP caliber player. And we only got 1 full year out of him. So, is it unreasonable to ask 12 mil transfer fee to start negotiations with Liga MX? I don't think so.