I think OBE's post above sums it up for me. We're in different places as clubs at the moment. It's a lot of money and some of the players on offer are quite decent. We need more decent players. We could use money. It makes a lot of sense to me.
It's my own personal opinion that 30m for Milner is more than fair, and more than he's worth. Could we replace him with the money? Maybe, maybe not. But I don't think our midfield was good enough to make the top four this season, and that was with Milner. I think his personality and work-rate have blinded some people to the fact that he doesn't have world-class technique or talent. This is not a player on the level of Fabregas here, and yet Fabregas is rated at 40m. It's insane, for me. Our strength this year was our defence. Milner wasn't carrying the team a la Fernando Torres or a Ronaldo. Our team won't be much different without him next year. We'll be worse off without him, but how much worse? It's hard to say.
My problem with selling Milner is more the message it sends out to the squad. Our hard work and chemistry is a large part of the reason we've been successful over the last few seasons. Selling Milner might make the squad defeatist. 'We had two goes at 4th, didn't quite get there, and we sell our best players. Why keep trying?' I have faith MON wouldn't let that happen, but you can see where I'm coming from.
But having watched Milner all year as a Villa fan, would I be terrified of seeing him in opposition colours, as a Utd or City player? Ultimately no. Which is why I don't mind whether he stays or goes.