If you plan on doing planetary imaging I say it's worth it. I'd probably invest in the mono version and a filter wheel with filters if you want to get more of the WOW photos you mentioned.
ZWO ASI120mm-s $179
ZWO filter wheel $88.00
ZWO LRGB filter set $88.00
I don't know if you want to invest this much now but as far as astrophotography is concerned this is not a huge investment.
But as someone mentioned above it is an endless investment. I don't know what mount you have but tracking is important. And I'm not sure if 900mm scope is enough for planetary imaging. (I don't know the sensor size of your phone but I imagine it is small so that the image is highly cropped - correct me if I'm wrong).
I have done planetary imaging with a similar color camera from Celestron (Skyris) and yes, I don't think my images are that much better than the ones you took (they are better, just NOT that much better).
Anyway, it is impressive what can be done with a phone camera nowadays. Good shots.