Even city would'nt pay 38m for Alexis. On his current form 10-15m is the max we can get on him. Transfermarket is not always accurate
Talking about sunk costs- If a club keeps a player for a longer time they can recover some of his transfer cost in terms of his performance(match or tournament winning winning goals, shirts sold etc) hence letting them go early before the end of contract will cause a loss. (But alll this doesn't apply to Alexis as he's not adding any value :
But Barca seems to think he'll come good)
Right, what's your point? You are saying Alexis has no playing value to Barca, so with that logic, they wouldn't be losing anything by selling him. I think other teams think he could have a lot of playing value to them like he did for Udinese, so they would be willing to pay close to what Barca paid for him. We could sell him for a lot, and certainly a fair bit more than Villa (mostly because Villa is so old, so there is less potential performance benefit from him).
Let's say we need to sell one of these guys to buy Neymar (which is the proposition I was initially responding to). Here are our concerns: We want to get a lot of money for the player we sell. We also want the player we keep to be one that performs well. Alexis can be sold for more than Villa. You also say Villa performs better than Alexis. If both of those things are true, there is NO reason to sell Villa instead of Alexis. We'd get more money if we sold Alexis AND be left with a better player still on the team.
You might say that Villa plays better now but there is a reason to sell Villa instead because Alexis is younger. However, you still say Alexis is not good. If he is not very good, and we get Neymar, then it won't matter how young Alexis is. Neymar will easily take virtually all his playing time within a couple years, and Alexis will likely be moved on at that point anyways. In that sense, the long term benefit of keeping Alexis is not better than the long term benefit of getting Villa (who would likely retire within a few years) because both would be gone in a similar amount of time. Of course, the logic is different if you believe that Alexis will become quite good with time, but then that's a reason to play him now instead of Villa (allow Alexis to reach his potential), so I don't think it's an argument you would want to make for your point.