Quarternion,
The idea of doing a SE IR appealed to me but I don't think the ATPLs will last beyond this licence issue. ie you still have to do the twin IR within 36 months of passing the ATPLs. Also the course is the same length and since only the last 15 hours of the rating are on a twin the cost difference is not as big as it sounds.
Also once you have the twin IR you can then renew on a single for 5 years before having to do it on the twin again.