I very much agree that it doesn't have to be one or the other, and that we need a mixture of both. I also can see how you say Fellaini ticked two boxes whilst Donovan only ticks one.
But how many boxes did Bilyaletdinov tick? Zero IMO, because his sell on value represented a loss that was similar to the loss we will be talking about through not being able to sell Donovan at the end of his career. That's the risk with this strategy, it CAN go horribly wrong.
It's all about balance, and I think we are currently at a point when we have enough players who have re-sale value,and that we need to invest in a seasoned professional who we know can come in and do the job that we want him to.