Right now there is almost nothing worth mining beside ETH and ETC. With XMR its mostly geared towards CPUs. So when you can no longer mine due to the large DAG you are out of luck. Your best bet is to list it on Craiglist and some gamer will buy it. You can sell the 4GB for like $70 and buy another second hand 8GB for like $90-$100 or so from another miner. Most gamers don't need GPUs larger than 4GB.
I don't know what is going on with ProgPOW, but if the switch is made then maybe the DAG will be removed or calculated differently , so maybe hold on to them for now and see what the future brings. However even with the ProgPOW eliminating or reducing the DAG, the price of ETH in general needs to increase for it to be worthwhile. Currently there is almost no profit unless you are hodl'ing for years to come. When it almost reached $300 it was pretty profitable for home miners but now it looks like it might retest the $100 area again depending on what the stock market is doing.
There are many coins to mine with less than 4GB of ram but keep in mind their profitability is much lower than ETH and ETH already is not that profitable.
Go to
https://whattomine.com/Put in your hashrates and see what is out there.
There are many Daggerhashimoto coins which you can still mine with 2-3GB GPUs, but keep in mind they are very unprofitable. Almost to the point where you are better off just buying an RX 470 4GB second hand since they are dirt cheap these days at $75 each.
