Just a note---if you're scaling by a lot (here we're talking 30-50% increases in grain bill based on the original figure of a ~1.045 beer coming in at 1.030, which is huge), just scaling each item in the grain bill may not work as you'd expect. Things like crystal, dark roasted malts or grains, etc, which do not require mashing, are probably giving you better efficiency than the mash overall. If you double them, you're likely to throw the recipe off. It's hard to say exactly what to do, but I'd be more inclined to increase base malts by a larger proportion.
You also have to deal with the effect of a thicker mash on the process---you'll probably have to add more water, and then boil down to hit the same volumes, etc. So while in principle it's easy, getting just the same result is hard. In that sense, I agree with your main point that fixing the efficiency problem is the best solution.