Sonic Se sound quality

Hi - I’m looking for advice from someone with a lot more experience than I have on virtual instruments. I’m using Cubase Elements 6, and I use the virtual instruments (Halion Sonic SE for bass guitar and Groove Agent for drums) that came with Elements. (I’m doing folk-rock kind of songs.)They don’t seem to sound that great, but maybe it’s just poor mixing, I don’t know. My question is, is the sound quality of those instruments poor? Or put another way, if I bought decent virtual instrument software, would I be getting noticeably better sound quality, or just more variety and features than I have now? I’d appreciate any opinions on this. Thanks.