This is a bit of a pie in the sky idea, but I'm throwing it out there in any case... With the ruler on, you can enter exact dimensions, which is great. But more often than not, when you do this, you are doing calculations at the same time to make sure you get it right. It would be great if you could build a "calculator" right into the dimension editor, e.g. when I enter a width of "50+30.5" it would automatically set it to 80.5. You really only need to support basic functions like (), +,-,* and /, but also allow multiple statements, like "25 + 7.3 + 5 - 12.8". It can replace the formula with the answer as soon as you complete the edit, so if you click on it again, you are just editing the single number, and not the original formula.
Also, it would be great to be able to actually enter the angle when rotating. The number comes up, but there's no way to click on it (it disappears when you move your mouse off the rotate arrow).