The extra damage dice is definitely fast and easy Svs.
I still like the idea of added damage in enclosed spaces though. Both myself and my co-GM are old SR players so the chunky salsa effect was the exact inspiration for that House Rule.
As for complication, I can see your point. In effect though, a grenade either hits or misses. If it hits, it blows the hell out of at least one target. To be honest, we've written that House Rule but we almost only use it on direct hits. For some reason it offended the heck out of both of us that you could drop a 'nade in someone's lap and have them shrug it off.