Welcome to Flyertalk tim131, welcome to the BA forum. Thanks for posting here, and I hope we will hear more from you - welcome on board.

Now you won't get Aer Lingus flights online (yet!), you need to call but they can be relatively inexpensive in economy, which otherwise isn't good use for Avios. Availability may well be restricted. DUB to BOS is indeed the cheapest way, 12,500 Avios for a single ticket. So you have got enough Avios to get both of you to BOS one way. Going to Florida pushes you from band 4 to band 5, thereby making it 20,000 Avios single each, so quite a cliff effect there.

My understanding is that these two Avios bands stay the same for Aer Lingus/US/AA for bookings made after 28 April. For BA metal they come down in offpeak periods from 20 k to 13k in band 5, but the carrier surcharges will be a lot higher on anything other than AB or EI.

Generally it isn't good value to buy Avios straight out. There may be a case for using it to top up a bit. There will apparently be a special deal tomorrow on Avios.com (for which you will need a UK address) which gets them at just over 1p each, and there is a similar offer with Iberia (for which you need the account open for 90 days), ending today, which is also about 1p each, payable in Euros. Both only get 1p per Avios at the top end of the buying scale, and it's not brilliant value. I tend to extract 3p per Avios value, and single revenue tickets are in fact a good use of Avios since they are more expensive than returns (generally).

Have a look at the Dashboard to research Avios in more detail.