> I have to think about whether I'm typing in TeX or iTeX

Actually, you don't. If you always space stuff out that shouldn't go together then it will look right in both TeX and iTeX. I started doing this anyway to avoid my spell-checker complaining about things like `dx`, but it's also good TeX style to separated things that ought to be separated. In maths mode, TeX **ignores spaces** that you put in because it knows better where to put spaces and how big those spaces should be. That's why you have to use commands like `\;` and so on to override TeX's spacing algorithms.