In order to make GUI program more maintainable, I would advise using approach of separaing GUI design and logic.

I mean approach described in http://www.vkonovalov.ru/vtcl-usage/Using_vtcl_for_creating_Tcl-Tk_GUI_for_Perl.html

It is not perlTk, but, in addition to pure Tcl, there is a possibility to use perlTk syntax, so most of code will work unchanged.

I am not sure whether you're going to redesign your GUI in VTCL, but you could try using this approach for new applications.