How important are GDL/LPC grades in the long-term? I’m not sure whether to pursue other activities instead.
I would imagine a little more weighting might be placed on the GDL but I’ll reserve giving any opinions on that, I didn’t do the GDL and I don’t want to advise you incorrectly. I would suggest putting the work in for the GDL, it’ll make the LPC easier because the content will be new, and set you with a good foundation of the law, which I do think is useful for practice (in a broad sense).
If we’re talking about law firm recruiters, they may care more about certain GDL grades such as contract law because that’s more important for commercial law firms. That said, if you don’t get a distinction in your GDL, it’s not the end of the world by any means!
With regard to the LPC, just make sure you pass and that the law firm doesn’t have any grade requirements. Post-training contract, I don’t think it’s important at all. Your undergrad matters and you’re all set with that. I’d actually strongly recommend using the time at law school to pursue any extra-curriculars you’re interested in. Free time will be relatively scarce once you start working. If you’re at the University of Law, feel free to drop a message on the board and I’ll send you some LPC notes.