Whatever someone is willing to pay and/or the seller is willing to sell for. Some items that are so rare that they don’t have ‘present day value’ to them, it as simple as that. Unikarp is borderline that category. You’ll see some past sales and have a few on the market per year, but it’s not reliable to deduct a definitive value from it.
As for the wich to go for between tropical wind/unikarp, I would go after whichever available in the best condition. They’re vary similar in terms of desirability and availability.
I totally agree how there’s no “present day” value to unikarp, but I am having difficulty gauging the price difference between a PSA and raw copy of the card. I am in talks of getting a PSA 8 from someone and just contemplating whether to pay a 1k premium on the PSA 8 or to simply buy a raw one and save 1k.
For Unikarp I would consider a PSA 8 to be a high quality card. Even five years ago they were difficult to find in good condition (Near Mint or above). I don’t know what you’re comparing to decide if it’s a good deal or not, I don’t know your personal goals are, what you personally find satisfying in your collection, or your money situation to help make your decision, but you do so it doesn’t matter what anyone says. You’re the one with all the info and what you should do, just be confident and no matter what you do you’ll make the right decision for you.