Just to add to the math, it really depends on what you own already and your capabilities to install mods yourself. Buying 3 pixelfx HDMI mods (shiny editions) will cost you around the same as the 4k (and that's if you can install yourself). Same thing as the analogue consoles if you want individual systems to play cartridges.

To add to the quality aspect, I have a 4k and I compared my RGB N64, HW1 N64Digital HDMI and RGB outputs, and Mister core as soon as I got it. The 4k looks better on my OLED than the HDMI output of the mod, with the only exception being if you prefer the smoothing filter in certain games.