Mike, I so know where you're coming from! I just spent a week in Germany for work, eating totally different things to normal, large lunches, meaty dinners, unusual carbs like pretzels and thick noodles, and my sugar levels were terrible! My average has gone up to 8.9 when I previously had it in the low 7s!
I think the adding a third insulin for large meals is probably about right. Just wanted to add that I also have difficulty with smaller meals than usual, e.g. I would normally have about 65g carbs for lunch and take 6U (ration 0.9/10g). If I have a smaller meal e.g.30g carbs, then it always seems like I don't take anough insulin and have highs later on. This happened on Friday, but then the highs could have been caused by the fat in the meal, as it was very cheesy. Have you seen this too?
But, in answer to your question, I could never stick to an "eating what you know works" diet, I enjoy trying different foods too much! I tend to just use lots of corrections when I'm doing something unusual.