This is true to some extent - however:
there is not really such thing as redundancy in modular - I have both and find that I use Rings in Easter Egg modes and Plaits in other modes often enough to warrant having a DIY Elements in my backlog - which I am hoping to get to before the end of the year! but then again I do have quite a decent sized modular - saying that I also like using both in similar modes at the same time
I would agree that a third sound source would be a good idea - something analog - personally I like the Doepfer Basic VCO and Buchla style oscillators
neither Rings nor Plaits is an oscillator - they are more self-contained voices, as neither needs a filter or vca after it!
"some of the best base-level info to remember can be found in Jim's sigfile" @Lugia
Utility modules are the dull polish that makes the shiny modules actually shine!!!
sound sources < sound modifiers < modulation sources < utilities