The Andy Carroll quip is not worthy of you. The logic in the cases of Suarez, Baines and Fellani is obviously that their subsequent performances have increased their value. A point so obvious that it was not even worthy of you to bring up, let alone attribute to me as arguing 'Well we paid £35m so now you must pay £50m, despite the fact that he's only worth £12m.'
Let me clarify what I consider a joke bid as this may be where we disagree. It's a bid where as a fan of the selling club you are saying to yourself, 'Fuck off, we would never sell him to you for that price. Why are you even bothering to bid?'.
Let's say the risk of a Suarez ban knocks £10m off his price. Leaving aside again your traditional rivalry and Real's bid which is just Madrid being Madrid.
Would you consider a £40m bid for Bale from Arsenal a joke?
The factors are the same, lengthy contract so no need to sell cheaply, one of the best players in the league, selling to a direct rival for a champions league place.
Also it was £28m for Baines and Fellani, £20m really would be beyond a joke.
So we're agreed that current value has nothing to do with previous value at least? The Carroll point was really just an illustration of that. What you paid for Suarez is irrelevant (other than perhaps to make the point that actually you paid quite a lot for him, which is why the gap between that fee and his current fee might not be all that much).
Also, the Arsenal comparison is not quite fair. You're not dealing with Everton or United, and you're really don't have the same kind of rivalry with Arsenal that we do, nor are you honestly competing with them in the league like we are.
But all that aside, had the Madrid thing not kicked off and Bale's valuation gone into the stratosphere, then I'd probably consider Bale to be worth between £50m and £60m, and thus a starting bid from a team like United at around £40m would have been pretty reasonable yeah.