That's what I do (s/Python/Tcl/). I feel pretty comfortable doing it, but a -little- uneasy. I feel like I'm cheating; I usually prescribe (and follow) "as dumb as possible (but no dumber)" rule, and use /bin/sh as my interactive shell to keep from relying on non-portable "creature-features". Using /bin/sh satisfies the "as dumb as possible..." rule because it's basic, standard, and everywhere. However, as soon as a shell script starts getting moderately complicated, I feel more comfortable moving to something (Tcl) that's (to my mind) less obtuse and less surprising.
To my mind, the "dumb" tools are the simple ones that often ship w/ Unix, and using them forces understanding of principles, rather than rote memorization of meta-commands. From that (the hope is that) one can _understand_ what a problem is, and now to fix it.
edit: and then I read http://news.ycombinator.com/item?id=2271004 further below, which makes Tcl (or python, or ...) look even better.