We need to spend big on full-backs. If I had a pound for everytime I read/heard "£15m for a full-back?" when we were hunting Alves, but fuck me, he would have easily been worth that. I'm sure of it.
I'm gonna stick my neck out here and I'm sure people are going to call me bonkers for what I'm about to say, but I don't think Arsenal would have been in the title race for as long as they were without Sagna and Clichy. That's how important full-backs have become in the modern game, for me. For starters, full-backs make ok wingers good and good wingers great. People will point to how United are on the brink of a potential double with a makeshift right-back, but when you have Cristiano Ronaldo in front of you, the only role you have is to cover the gaps he leaves, rather than exploit the ones he creates.
For us, it's necessary to get quality full-backs in. Riise must go ASAP and we mustn't be afraid to throw serious money (if we have it) into this area.
However we may try to convince ourselves otherwise but we missed the ship by not getting Alves. Benitez decided to spend the budget on Pennant and Bellamy but £12m would have been better spent on Alves. Oh well, it's easier with hindsight.
I would love for us still to pick him up, even if it is for the £15m you have quoted. As you have said, full backs are very important in the modern game. It is funny how you have used Arsenal as an example because they are the side who I feel revolutionised the full back's role. The amount of times the likes of Lauren, Cole, Clichy etc. have been on the end of final passes in moves is unbelievable, normally setting up the player who is supposed to be the 'winger'.
Our full backs get into decent positions but it is what they do once in those positions that is the difference. Bar Aurelio we do not really have full backs who can deliever on an attacking basis. Unfortunately, Aurelio is made of glass.