Originally Posted by Gardyloo

In December you can buy a round trip ticket from BOS to Dublin for around $700, where an LONE4 will cost around US$3250 plus taxes/fees.

You could either head west, then finish back in Dublin before your flight back to Boston, or you could reverse your route and "stop over" in Boston for a long time, and maybe use your North America legs during the balance of the 12-month validity period of the ticket. In that case, you'd probably want to buy a one-way ticket to DUB (around $500) and use miles or points to get back after finishing the RTW.

Westbound - DUB-PHL-LAX-MEL-CBR-MEL-AKL-MEL-DXB-LHR-GVA-LHR-DUB
Eastbound - DUB-xLHR-GVA-DOH-DXB-MEL-CBR-MEL-AKL-MEL-LAX-BOS-(MIA-BOS?)-PHL-DUB

(I.e., you could squeeze in another trip from BOS before ending back in Ireland.)