I honestly wouldn't use them, I'd basically just collect refunds indefinitely. Most of the skins that I have and don't want/use are from my addiction to mystery skin purchasing, and you can't refund those anyway.
Each rune that I own are used in some degree in at least a single rune page, excluding some really specific ones that just got phased out when I stopped playing Soraka, but they're still there for if I ever pick up the champion again. Acquiring all champions was useful for champion swapping in champ select, I can now trade anyone any champion they want from whatever pick order as long as they have the champion as well, it also means I have no issues about trying out anything that seems interesting to me. The skins I have are all interesting within their own right and I don't regret having any of them, as again, the ones I'm not a huge fan of are from mystery gifts/mystery skin buys.
Furthermore if I actually went out of my way to purchase a skin, like Bloodfury Renekton for example, I know that future visual upgrades to the skin, will most likely simply make the skin better in appearance while maintaining it's original theme as closely as possible. Poppy skins for example are all better than their previous form, to the point where I purchased Noxus Poppy despite not being likely to play the champion very much. There will still be moments where I may dabble with the champion, or it might be a pretty solid pick in a certain situation.
I read one of your posts to another person on offering guarantees. Apple wouldn't have people purchasing, if they didn't offer a guarantee, which is true, but they also don't provide any sort of product for free on which that guarantee exists. People forget that this game is entirely free, slight speed ups in progress, the ability to accelerate your purchase of champions, and the chance to customize your champions' appearance through alternative looks are available, but none of that is required, you're perfectly able to not spend a penny on the game if you so desire.
Guarantees aren't typically offered for free on any product, it's part of the reason a new iPhone runs $600, they've already covered the risk of having to send out another one. In fact I'm pretty sure the iPhone 6 only costs the company $200 to manufacture, to then sell it at triple the cost, you've covered the cost of the initial product with $400 profit assuming you don't have to send out another one, and if you do, you're still coming out with a profit equal to what it costs. To have to send out two phones under that guarantee to a person you still break even, but are likely profiting on a large number of other people. So believe me those guarantees are not out of their faith in the product, they've already hedged their bets through the cost of the product.