I rarely see premium economy fares for this kind of price, but if you can get to Madrid and want to fly to New York you can do this on a mix of Iberia, British Airways or American Airlines for a VERY tidy sum of just £482 or €539.
You can travel on this fare nearly anytime between October-November 2019 (subject to seat availability) and between January – May 2020.
If you route this with a stop in London then you can get 110 Tier Points each way, so 220 on a return trip. At £2.19/TP this puts it into a very solid earning rate. While not quite on par with the recent £1.31/TP of Helsinki in the latest sale, it certainly makes a nice alternative to shuttling back-and-forth.
Being a genuine long-haul route too, this would net you a very good chunk of Avios – around 8000 Avios as a bare minimum before you added elite status bonuses.
If you are an American Airlines AAdvantage flyer this makes for an excellent Elite Qualifying Miles and an Elite Qualifying Dollars fare, as it would be calculated based on distance flown rather than dollars spent. (Approximately 20% of the total, so around 700EQDs)
I was able to construct the headline fare going using 4-11th February 2020 as test dates on Iberia.com,
As this is a British Airways / Iberia/ American Airlines joint venture fare you should be able to book it on any of the carriers you want, which will help if you need to use your credit card on any particular site. For most readers of this blog it will probably be ba.com.
There are further optimisations possible using the MPM ticketing rules but the added time for the very little added benefit doesn't seem to make it a great fare to do that. You could add in an extra transfer at Boston if you desperately needed that extra sector.