I'm finally done with this
just got my "carta de ciudadanía" this morning. I started the process in June 2020, so it was affected by the pandemic, in both positive and negative ways, so it took 2 years and 3 months. It could have been faster, there were opportunities to move it along more quickly, but they weren't taken. I had a lawyer; however, as dsp27 and others have demonstrated, it's not absolutely necessary.
I'm holding off applying for my brand new DNI for 10 days or so (I have a foreign trip coming up shortly), so I can report on that part later. The initial feedback I got on two points was: 1. the "auto de identidad" referenced by bajo-cero a few pages back is redundant, due to having the old DNI number printed on the back of the new one. 2. I don't need a "certificado de domicilio" to have the correct address on my new DNI, I can just state my current address at RENAPER when I go there for my DNI.