Well, the point with modular, as far as I am concerned, is to be able to connect "characteristics" of your choice. One set of modules in a setup each have distinct characters, compared to modules in a different setup. This is sort of the point of modular. With two setups or more, or just a larger set of modules, you can combine the individual modules and generate unique timbres. So where does one draw the line then?
The crux of course, is to know whether a module directly compares with one you already have. Most modules likely try have something unique, but the difference can be very subtle, and not worth the expense. On the other hand, and unfortunately for any owner, there are also times when you find a module that is basically the same as what you already got, but with one or two features/capabilities that makes it difficult to justify not exchanging modules, which becomes expensive over time.
There is a recent video from Pittsburgh modular about their 'Primary Oscillator' in which the person states somewhere along the line of, there are so many modules that produce the typical analog waveforms that we wanted to do something not done before. This, to me, sort of reflects on the point of the above. Of course, people will argue until the end of time whether two modules are basically sound the same (or not). Nuances, oscilloscope readings and subjective variety. You have to do a bit of research yourself.
Personally, I would go for something that you do not already have. Meaning, if you already have something that will basically do for you, what the Dixie II+ will do, then why get another one? People will argue for and against this and that, but the bottom line is that it is your money, not theirs. If you are going to spend on something, go for what is going to expand your sound palette.
Or look at it this way, why BUY two shades of blue, when you can mix the one shade of blue with something else and make your own shade of blue? Perhaps if money is not an object, but then what is the fun in that. :) Why not get yellow, which enables you to make your own green, and so on.