If you need a finger in the air valuation for Avios, you can't go much wrong with 1.35p. That's the current promotional price you can buy them at.

On the basis you can pick up sale fares to NY for around £1500, this makes sense. 1.35 x 80,000 plus £500 of taxes is as near as matters £1500.

If you try to put a LON-DUB and DUB-BOS flight on the same ticket, you will have to pay the UK departure tax, thereby mitigating much of the benefit. You'd be better off flying to Dublin the previous night and staying in an airport hotel.