The value depends on what the alt or alts can do and on subjective value the player puts on the ISK.
You really do not understand this do you? Value in economics is largely subjective–i.e. it depends on the person in question. I might value something you see no value in.
As I indicated it is largely subjective. That is why if we have two players with identical alts one for say PI and the other for cloaky camping one player might pick cloaky camping the other the PI option.
Yes, that is part of it.
Even if the cloaker is an SP farm there is still an opportunity cost, because he could be used for something else to generate ISK over an above SP farming. The SP farming does not negate opportunity cost although it may change the calculus for a given player so that AFK cloaking becomes preferred.
Again, this does not change anything at all. The fact still remains that either that alt, or another alt could be used to generate ISK and that is not possible if the cloaker is logged in at a safe and cloaked.
Yes, he does. Suppose you have a $100 million trust fund and it generates $3,000,000/year in income for you. After taxes lets say you have $125,000/month in income. You can also either spend all day playing video games or go work for say $2,000/month. If you opt to play video games your opportunity cost is the $2,000 in work income. The $125k/month may change the cost-benefit calculus for you, but it does not negate the opportunity costs. It is just that the marginal benefit for additional income from working may not be worth the effort relative to playing video games.
That some people are willing to incur this opportunity cost does not mean it does not exist, it just means whatever benefit they obtain from AFK cloaking is greater than the opportunity cost. Maybe this guy with 25 accounts absolutely loathes grinding for ISK and IRL his income can let him skip it and he can park 25 alts in 25 different systems looking for a fool.