Is Tkinter worth learning?

The answer to your question is a resounding yes.

Qt is good, I have nothing against it. But Tk is better and far easier to use and quite well documented - not just on the Python webspace, but there are also many third-party tutorials out there. This particular one is where I learned it from and it has been quite infallible in serving me.

You might want to take a look at this(wxPython).

wxPython is the best and most mature cross-platform GUI toolkit, given a number of constraints. The only reason wxPython isn't the standard Python GUI toolkit is that Tkinter was there first. -- Guido van Rossum

As a step up to other GUI toolkits, sure. If you know other toolkits then you already understand TkInter and can leave it until you actually need it.

Why not go for PyQT? You apparently are already familiar with Qt, so it should be relatively easy to learn. In my opinion it looks better than Tkinter, and it sure is better documented.