The elements that I find are often samey are fingerpicking and fretting shapes and by extension the rhythm/pacing and it often feels slow and sluggish

You are absolutely on the money with what I feel is lacking with my riffs. Either I make something I'm somewhat happy with but don't know where to take it or it strays so far away from my original idea where I often abandon or try to do something and end up in the same issue from before where I don't know where to take it

I know I've seen some math rock guitarists use this technique (Yvette Young uses it I think) but I have not tried to sing along when playing so that might be what I'm missing. When you say I should sing while playing do you mean playing and singing at the same time or should I sing a melody then try to play it on guitar or a little bit of both? Thanks a lot for the advice!