I used to advocate trying to do good work on LW. Now I'm not sure, let me explain why.
It's certainly true that good work stays valuable no matter where you're doing it. Unfortunately, the standards of "good work" are largely defined by where you're doing it. If you're in academia, your work is good or bad by scientific standards. If you're on LW, your work is good or bad compared to other LW posts. Internalizing that standard may harm you if you're capable of more.
When you come to a place like Project Euler and solve some problems, or come to OpenStreetMap and upload some GPS tracks, or come to academia and publish a paper, that makes you a participant and you know exactly where you stand, relative to others. But LW is not a task-focused community and is unlikely to ever become one. LW evolved from the basic activity "let's comment on something Eliezer wrote". We inherited our standard of quality from that. As a result, when someone posts their work here, that doesn't necessarily help them improve.
For example, Yvain is a great contributor to LW and has the potential to be a star writer, but it seems to me that writing on LW doesn't test his limits, compared to trying new audiences. Likewise, my own work on decision theory math would've been held to a higher standard if the primary audience were mathematicians (though I hope to remedy that). Of course there have been many examples of seemingly good work posted to LW. Homestuck fandom also has a lot of nice-looking art, but it doesn't get fandoms of its own.
In conclusion, if you want to do important work, cross-post it if you must, but don't do it for LW exclusively. Big fish in a small pond always looks kinda sad.