So far xschem with gaw as the viewer seems to be pretty decent.

while for digital wave viewing there is a solid tool, gtkwave, for analog waves there is really no 'good' open source tool. To this aspect gaw (a fork of gwave) has some improvement, but for big designs it shows its limitations. (flat signal list).

Right. The author of glscopeclient, Andrew Zonenberg mentioned that he'd love to see his client be retrofitted with support for reading ngspice simulation data (and possibly vcd and fst as well, but we have gtkwave for that as you say so not as "urgent"). I think glscopeclient is really cool; https://twitter.com/azonenberg/status/1312896522283937792

Looks cool. I think ngspice raw data file is really simple so i hope it will be added soon... Btw i also have a .raw -> .vcd translator that allows to see ngspice simulation in gtkwave. See video. Translator can be improved is there is interest in it.