Just like Jam,Opeth/PT (and pink floyd) were the bands that made me want to pick up the guitar,after playing bass for nearly 20 years i was feeling a little bass'ed out and need'ed a break from it,so i decide to buy a few guitars & spend a bit of quality time on it,now after nearly 2 years spent with a 90% of my playing time on a guitar instead of a bass i have a new found respect for both instruments.
Im not saying that you cant learn all you need to know about harmony and melody on just the bass but for myself (just like Hobbayne)i found things to become much clearer after playing guitar for a little while,it also got my fingers out of there bass pattern rutts,im not saying that i now play bass like a guitarist but i no longer play guitar like a bassist if that make sense,& anyone who thinks your betraying what it means to be a bass player just because you picked up a guitar for a while really hasn't got a clue.