|Do you know where your variables are?|
Providing a prosaic description of your code, rather than actual code, is an exceptionally poor choice. This greatly hampers our ability to provide improved code. Please don't do this. See "How do I post a question effectively?" and SSCCE.
"Is it possible to disable the GUI Event mechanisms, ..."
Check the documentation on a widget-by-widget basis. Interactive widgets often have a -state option, with possible values such as disabled and readonly, which may be sufficient for your needs. For greater control of events, try Tk::bind (and do follow the additional links at the end of that page).
"Is it possible to disable the binding of variables to widgets, like -textvariable for Entry widgets?"
I expect you mean something else. The obvious answer to your question is don't use a -textvariable option. If you meant "delay" rather than "disable", see Tk::options.
"I have already replaced some really slow superwidgets for leaner alternative (e.g. JBrowseEntry for BrowseEntry) but maybe there are leaner widgets still?"
Maybe there are. Without any code, how could anyone tell which widgets you consider slow?
Again, no code, no answer possible.