I am not having much valuable cards on Splinterlands. However, the current value of my cards is around 130 USD.In the last season of Splinterlands, I got Silver III position. I got cards worth $6.8 as end of the season rewards.
As you can see above, I also got some DEC and potions. I am happy with it. Especially, getting a legendary card is always a good thing. Last month the value of my cards were around half of the current price of my cards. So, it is increasing. So, investment on Splinterlands is a great option and also it is fun to play the game.