It's a game. For us, it's not about taking risks with your character, but having fun with the other players.
The latter I assume as a given, regardless of anything else.
The former, if not done, makes for a very dull and boring game; thus IMO it's worth rewarding as a means of encouraging it to happen.
Absolutely. We've played in groups where the character levels are all spread out because of differing XP awards. We found that it simple encourages 2 behaviors:
1) PCs doing things just to earn XP (i.e. I search for X, I do skill check y, I talk to the bar maid, or whatever other incidental the DM gives XP for)
2) Players leave because they are being punished (not given XP) for playing the way they want to.
It's not fun for us. But each group's gotta find what works for them.
I've no problem with 1) here; if it's encouraging the players to have their characters do things, that's good; even if it's "just to earn xp" (which IME only happens when someone's within a trivial amount of bumping anyway and just needs that extra few).
I see 2) as a problem-player symptom. At its root, the game - whether played as Big Damn Heroes, murderhoboes, melodramatic story arcs, or whatever - is about characters either getting things done or dying in the attempt; and a player who won't engage with this root premise is a problem.
Also, it depends on what one sees xp as. For me, the word "experience" is key; they're reflective - in an abstract way - of the character learning and growing through what it experiences, usually in the field. Thus, perhaps obviously, a character who doesn't take part in those experiences doesn't get the resulting xp.
Now if this was a discussion around 3e or 4e I'd be somewhat more sympathetic, as those editions really don't handle split-level parties very well. But 5e does; as do the TSR editions, where variable levels within the party was almost a baked-in assumption.
It works really well for us. I actually started it because 1) I always forgot to award inspiration as a DM, 2) players never used it because it was hard to come by and not top of mind. Now it's something they think about every session, and at the end of the night the re-live the coolest moments as they nominate folks. "Aeroian for when he jumped on that crabs' back!"
Again, I like the idea behind what you're doing; but I very much dislike that sort of meta-currency in general - far too small-g gamist.