I use the compose key a lot; when writing docs I tend to use → instead of ->, I use – instead of -, etc. I have an extensive XCompose set up for all this, and I find it very convenient.

But it's still three keystrokes instead of one. I wouldn't really look forward to using × instead of *, ÷ instead of /, etc. all the time, even though I can type them here with relative ease the hassle increases the more you use it (I don't tend to bother with fancy “quotes” for example).

I also don't think it really matters all that much. What's wrong with *? Sure, × looks nicer, but * is clearly the pragmatic choice.*