I hope that @Awwburreee is OK. Haven't heard from the OP after the first post.
I think maybe we scared him/her away ???? Hope not....
Seriously, you give a pro or an advanced player a humble Selmer Bundy and they play a gig with it. Few will know what sax they are playing. Their riffs, everything will sound pro. Some pros even use a "busking level" student or intermediate sax to play in venues where they don't want to risk damage to their higher cost axe. The character is in the musician. The sax is a tool.
Completely true. One thing to consider however is that the player, to play their best, wants to have the horn they feel most comfortable with...so they can play their best. Yes, the audience (of non sax players) wouldn't likely notice anything, but if the player doesn't feel the 'horn can do' what he/she is used to 'doing', that will effect their playing...note selection, phrasing, etc.
So the tool needs to do what the players wants it to. Some horns, in some players' hands, can't 100% or even 75%.
I DO agree with
@thomsax characterization of a "lack of character" in (most) contemporary below-pro level models of sax, actually....from the context of tonality. There is a 'modern tonality'...and on a Yani or high-end Yama, that can be quite a nice tonality. But going down the ladder of models/levels, there is sort of a certain 'sameness' in tonal attributes to modern horns. Just really the new sonic paradigm which Yamaha primarily ushered in in the 80's.
So revisiting the performer on stage example, even a non-musician would likely notice the difference in tonality of a Welt vs. a YAS-23. I do think it is ASIDE from that particular parameter that a Welt starts getting its butt kicked a bit....key action, overall feel under the fingers, for example...if those are your top checklist-items as a player, your top priorities.
Second thing, beyond key feel and action which comes into play between a German vintage and an Asian modern - is intonational flex - straight-arrow intonation is desirable by a lot of players....they wanna be able to slip up and get lazy in their embouchure and not have in necessarily show up in the notes. Easier to do on a Yani, Yama, Jupe than on a Weltklang or a JK or even a Conn. But this is also variable depending on the desire of the player.
I know quite a few really good players who set aside (either permanently or just on certain playing occasions) their top-line modern pro horn because they couldn't get the intonational flex they wanted as compared to their vintage one.
So "what you blow in the instrument determines what comes out" is true - and not true. An intermediate or above player will notice how a horn responds both under the fingers and to subtle (intentional) changes in embouchure (aka 'blowing'). It is a fact that a player can take their skill level and put it on a different horn and that horn will not give them the same result, so they are putting in the same input but not getting the same output. This variability exists even between student-level models of different mfrs....
So this starts going into things beyond "most people at shows or private functions aren't gonna notice". That is one yardstick and it is probably true. But it is also arguably not the end-all thing. Probably more important to the player is whether the horn can still output the way they want it to.
This thread is doing a pretty Deep Dive as far as the direction of the convo, actually (not digressing, mind you but opening up many facets) , the OP was just asking if a $400 listed Welt was a good deal....
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(With apology to Weltklang owners.) 
