keep in mind that the resale value will drop as long as the silicon shortage stop, or if the next gen arrives. so you'd either have to get roi asap, or hope that if you can't get a decent roi you can sell it before the shortage is over. while 3070 might be more expensive, the resale value might be higher.
Some models will drop in price like a rock. Mostly the higher end ones. As newer & better higher end ones come out and their value priced version equivalents the last gen will drop.
The mid range will drop to the low range price.
The current low range will drop a little for people who don't care.
i.e. I can get a new whatever for $149 or $129 or $179
I can get a generation or 2 out for $49 or $79 or whatever.
It's for the people who are not gaming or mining but just want something more then the onboard graphics that come with their PC.
It's actually why IMO the RX 5xx and 4xx were still around. I even had a pile for people who wanted something other then the stock Intel but did not really need to spend the money on a GTX 1650 / 1660 so they got those....
All the above is my opinion and pure speculation. Don't spend money based on just what I say, DYOR and form you own opinion.
-Dave