Only problem is I don't like selling stuff because I'm always being talked down. If I sell my six GPUs, someone will lowball me. I hate that. I sold a razor phone and the buyer gave a sob story and said it was for a senior to call 911. I tried to be firm at $50, but they kept to their sob story and only offer $30 and there were no other buyers. This is common on craigslist/ebay.
If you know what the market value of an item is, then offer it at a fixed price. No need to argue over sob stories with the buyer.
Continue mining until somebody buys the card or rig. Selling is not easy, especially in bulk; but seeing the value of your card drop from $350 to $200 overnight is much worse, let alone when I suffered a $370 to $90 crash in 2018. I price in a 15% loss when I sell anything due to either 8-9% feeBay fees or the time I spend.
If ETH can still be this profitable after all those millions of Asic miners around the world then its possible that other PoW coins will continue from where ETH left off, its only a matter of time, once every coins are worthless to mine the difficulty will start reducing, this is where I will get in.
I don't think ASICs are more than 30% of the nethash for ETH. Even if they are, the price of the ASICs is so high that building a GPU rig is better.
You are right that it will take 'a matter of time' for a new GPU gold rush, but be prepared to make zero daily profit for up to 3 years while you wait and your rig depreciates by 20-30% per year. If there is a gold rush, your rig doubles or triples in value while the coins you HODL'd go up 3-10x.
I would also only speculatively mine coins that are cheaper to mine than just mining the most profitable coin, then trading it for the coin you want. Usually it's cheaper and more convenient to just mine the best coin, then invest the proceeds into a portfolio of speculative coins.
