I would risk the same plane if it was the same operator with the same plane thereby guaranteeing that if the flight to Dublin was delayed/cancelled the flight back would be too.

However, I wouldn't risk another airline - my Aer Lingus flight to Dublin from London last week was cancelled. If I was in your situation I would have been left high and dry.

I didn't think the flights ex-DUB were as cheap as (say) ex-AMS/Italy generally?