I've been hoarding fest skins for 6+ years and IMO it's a really long return investment and not super worth it unless you have literal years to sit on them and don't want to invest that money in anything quicker. Desirable accents/skins even from years ago typically only go for 100-200kt assuming you can predict which ones people will like, and they sell slow. You can really only list 1 or 2 of each copy at a time, and if you want to maximize your investment you'll have to check fairly frequently because the price for each varies a huge deal even week to week. That said you can buy them and forget about them and they're a really low energy turnaround. Depends on your playstyle really