Sure I've read some comparisons and know the specs, but looking for some quick opinions from anyone with the knowledge and the time;

Been saving for a new and shiny 404sx, getting pretty close. They're like, 460euro. Have the possibility of getting a 'barely used' 555 for 300euro.

I was looking forward to the portability but the 555 looks so shiny, with extra buttons and whatnot.

Who thinks it's worth the trade-off?
Is it a good price?
Should I stick with plan A and get a new 404sx with warrenty etc

Depends on what features you want from which. If you did your homework on both, then you already know their pros and cons.

But if you're asking what you should buy, a barely used 555 or brand new 404, I'd get the 555. Anything left over you save for a 404, and if you didn't care for the 555, then you could probably swap it for a 404 easily!