But having walked from Lisbon in Nov/Dec last year I think I'm over all that (no people, little infrastructure until Porto, had a wonderful time).
Did you walk the Sanabrés after Zamora or the Francés? That would be a way to mix it up. There will be more people on the Vdlp than on any of the other routes people have mentioned, unless the Invierno gets a huge burst.
If you’re fine with no people, here are my comments -
I would second the Levante (very good albergue system, though probably not more than 50% of the places, lots of cheap pensiones, lots of very interesting small towns, Toledo and Ávila are wonderful). Merges with the Sanabrés in Zamora.
the Ebro — goes off and on along the river, few albergues, not as many interesting villages/towns as the others, Zaragoza is very nice.
the Mozárabe from Almería (terrific albergue system, Amigos in Almería who will smother you with kindness and provide incredible support), a chance to see Granada and Córdoba, two five-star places. LOTS of olive groves. Merges with Vdlp in Mérida.
The Invierno - parallels Francés to the south, starting in Ponferrada. Almost all in Galicia after the first day. Getting a big push from the government and a Brierley
guide, so expect to see more pilgrims. A few nice towns, lots of nice scenery, nothing spectacular like the Olvidado through the mountains, but nice.
Madrid will drop you in Sahagún in about two weeks and then you’re back on the Francés. Very rural, off-road (virtually no pavement), lots of albergues, some nice towns, but for me the best part were the days of wide open emerald green fields undulating in the wind, punctuated by big splotches of poppies. You may be too early for that, not sure. Segovia is a very nice place to visit, too.
Good luck, @Damien Reynolds