TLDR: If you believe in a future Caro Poison team, Xu looks to be a solid investment. She can fulfill her job in this regard even at E0, although you'll want to eventually get her to E3 or OE to further her Spellbound stacks/stacking. However, as of the writing of this it is unclear if Caro Poison will become a legitimate and powerful team, so you can safely skip if you're already satisfied with your current roster.
Xu is a Caro support who primarily supports Poison based teams. While she does have some Embryo Fusion and can reduce enemy STR, these things aren't particularly strong compared to our already available Caro supports (Thais remains the best at Embryo Fusion, and Pickman can drain STR while also dealing high AOE damage). Her ability to apply Poison is decent, but the main draw is her Spellbound effect. This effect, applied by either her Exalt or her Resonance enhanced Fan-Sealed Kiss Command Card, can be "detonated" by her Exalt to deal Max HP Fixed DMG (a very exclusive damage type only seen on Lotan's OE and GDoll's form change card) and trigger Poison. Considering you'll likely pair her with GDoll, you can probably see the sheer nuking potential Poison teams can do with this combo.
Before Xu's release, Aequor Poison was the only "viable" Poison team. Sure, you could do Ultra Poison with Liv but that team was clunky and difficult (AKA mald reset central). Xu opens up the lesser used but potentially powerful Caro Poison team, utilizing the Embryos as a way to further fuel GDoll's Exalt spam. This is especially evident with Xu's Devour being relatively lackluster compared to other recent Caro releases (though it can certainly come up, especially when fighting trash packs). Considering GMurphy's release effectively monopolized Miryam away from Aequor Poison, GDoll is looking kind of homeless right now, so Xu is a fairly natural pairing.
With that said, Caro Poison not only lacks a decisive team composition, it also doesn't really fix the issues that Aequor Poison had. High health trash packs continue to remain an issue, even with Xu having a decent AOE attack. While you can relegate them to fighting in D-Tide elite/boss waves, this does leave the team in an awkward spot when they're not favored against those waves or outside of D-Tide.
In terms of investment, Xu at E0 is generally fine. While E3 and OE are definitely things you should aim for due to how powerful Spellbound is (and GDoll makes OE very easy to activate in fights), most players will be able to sit on her E0 and find decent value until they can make that leap up. Her E3 and OE are very powerful, with E3 doubling the max stacks and OE applying a massive 5 stacks of Spellbound or even mass fueling your Crimson Furnace. Salvador's best support?! No, but it does give you a nice boost in survivability.
Ultimately, Xu is a fairly skippable awakener. While she is quite good for her archetype, her archetype isn't exactly breaking the meta or anything like that. It's entirely possible that future Caro releases will further push Caro Poison and make it a powerhouse, but with what is currently available I cannot see a world where Xu is a must pull.
