Yes. That (together with a || $x==1 && substr($x,1,1) ne '1') does exactly what I find myself wanting nine times out of ten. That is, what isNaN does in js. I'd find it useful to have a built in function, and maybe we're going to get one.
Hmm, when does a scalar convert to 1 when it's not a number?
Note that I didn't mention that you should already know that the value is "a string" rather than a reference or funky blessed overloaded object, but carefully worded it because I had that in mind.