The Dixie II is a very vanilla oscillator. Having a third oscillator isn't bad if you're wanting a three voice architecture. I'm not familiar with the Mother-32 architecture itself, so I would ask how do you intend to use this third voice and mix it into the signal flow of the Mother-32?
Once you have that figured out, you may want to go with the Rubicon II if you want to stick with Intellijel. It will give you more options than the Dixie and a ton more in waveforms. Plus it does "thru-zero", which may be something you're interested in.
If you're looking to expand the Mother-32, you may want to consider going for effects and modulation rather than another discrete VCO (unless you plan on modulating with that VCO). You can get some new sounds with the use of wave-folders, complex LFO generators, ring modulators, etc.
As to being a full-time producer, modular is expensive on the bottom-line in both cash and TIME. Playing around with Eurorack to get something you can cook up on a traditional synth isn't a very effective use of time. If you want something special with a bunch of unique modulation, then Eurorack just might be the ticket. But the biggest down-side is that once you pull your patches, they are GONE and can't ever be recreated exactly, even if you remember/document your exact settings.
Okay... that's all my opinion and take it with a grain of salt.