I have found "magic-space" more useful than ":p". This auto-expands history substitutions (like !$) when you press the space bar. You can bind it to the space key in tcsh or bash. It also works for !!, !vi, and other substitutions.

So, when you press ! $ <space>, it expands out to "foo" in place, so you can be sure that's what you wanted, and edit it in place.

I think :p predates magic-space. They're both decades old at this point though.