30 year olds hardly have sell-on value, so I dont know what you are talking about when you say we should "look for sell-on value with older players".
The same arguments on Gameiro were used regarding Arda. "he will be instant impact, who cares about his sell-on value, who cares about his fat 5 year contract, he is world class, proven La Liga player, great deal, important to focus on short term now that Messi is at his best so we can win titles". blablabla.
Messi has been the difference maker for most of our titles. The part about signing SOME players to make an instant impact (insert: see Luis Suarez) is very true. That mentality won us a treble that year. I don't think we would of won it if we had signed Icardi, Vietto or whatever fotm young striker was around.
Arda could of been a good signing, but he himself failed us. We thought we were getting ferocious Arda from AM..instead we got fat, lazy Arda who showed not a single inch of heart he had shown in previous seasons. Was he technically what we needed in the midfield? Maybe not either, but any player that shows that kind of desire to win like Arda in the past and Suarez is usually a good influence on the team.
The price wasn't Arda's fault, you can blame Barto for that.
We could of went for one younger CB instead of Vermaelen at the time, would of saved us 10-15mil I guess. Other than that I have been happy with Suarez and Mathieu our two older players we signed. Same with Bravo.
The time to buy some other young players is now. Sell Arda, buy a young promising CM and striker (Gabriel Jesus) along with the signing of Umtiti and we are in great shape. Perhaps a young LB who can play RB as well.