I wouldn't say it's obsolete. It is about 3-5% faster than the 1660 super which is the card I bought. When I looked and the performance % was so small, I didn't want to justify money for the 1660 ti. However, you notice how quickly prices dropped on the 2060 for example. You almost have to think nvidia was price gouging people until there was more competition.
I would say, I just looked on ebay under completed items. It appears the 1660 ti used is going for about 200-230ish US dollars. I found that by searching 1660 ti, and checking completed items.
If you wanted, I suppose you could sell your card as used. You'd take a bit of a hit on it, but then that would let you put a few bucks more with what you get for it, and buy a better card like a 5600 xt or a 2060. Or try to enjoy the card a while. At least on my 1660 super, for 1080p, it's not bad. I can see myself upgrading maybe in the next year sometime possibly. But it's decent for 1080p and even relatively high refresh rates say maybe around 100hz. Probably depends on the game. Been playing Battlefield 1 and about to subscribe to Origin Access so I can play battlefield 5.