You appear to understand why Fianna Fail has become so good at coalition governments (after their initial efforts), Fianna Fail, itself is the ultimate coalition. Those who view the party in very narrow terms such a the Builder's friends or the Publican Party, miss the point. Its reach and representation is far broader than that. Which means that it act as if it is in opposition, when it is in government.Stop trying to seek the demise of Sinn Féin would be one good way to prevent FF ruling forever. Many SF voters are soft on FF and Bertie Ahern to his credit recognised this. Hence his "moving north" stance. In the border counties especially FG are viewed as been slightly better than the Spanish Inquisition. Only slightly though and civil war politics are alive and well in many rural communties.
FF is a master of playing the opposition parties off against one another. They didn't really believe in the "we won't do a deal with SF" before the last general election but it was an excellent ruse that allowed them to make sure people didn't give SF transfers and therefore damage potential soft FF seats. If they had needed Sinn Féin they would have found some way to bring us into government. That is the strength of FF it mutates and changes to suit every situation. I don't admire their politics but I do admire their survival instinct. Perhaps if the rest of us in Irish politics had the same instinct we would spend less time on the opposition benches.