I wanted to ask if your Gameboy is celebrating and which one you like best and is it worth buying one more? And is it also worth buying a Gamecube?
I still have my Gamecube and would never give it away. If you like the games, why not?
Gameboy Advance SP
And Gamecube save because it was really good
Which Gameboy do you like best
Unpopular opinion but I prefer the GBA Micro. I like it for its tiny size so that you can always have it with you.
A little more popular and also my personal recommendation if you are mainly interested in the games then a classic GBA with IPS Mod would make the most sense because it is also compatible with Gameboy and Gameboy Color games.
and is it still worth buying the Nintendo Gamecube?
If you're up for the games, sure!
But you said you were concerned that the old consoles don't look as great on modern TVs as you remember them. So if you no longer have a tube TV, you should also invest in a sensible upscaler like the framemaster.