I've thought the same, so me and my players hacked it a bit.
Here are my houserules:
Throwing a grenade is the usual ranged weapons roll as normal (yes , that means you can make a quick shot with it, if you dare).
- Rolling a failure (no sixes) allows the GM to spend 1 DP to dictate where the grenade hits.
- Rolling a limited sucess (1 sixes) means you hit something, but not everything you wanted - your blast radius includes half of the people you were trying to hit (so limited success with a group of 4 enemies mean you only hit 2 of them).
- Rolling a success (2 sixes) means you cover all the combatant you wanted.
- Rolling an exceptional success (3 sixes) adds another +1 damage to anyone who recives damage from the explosive.
- Blast Power and Size works the same way as in the core book.
So far it has worked fine for us, but we don't have an extremely tactical game, so it might work differently if your game is more Mass Effect than Blade Runner.
I also think that allowing +1 damage for any sixes above exceptional would also be ok, it might make explosions more crazy, but ... they usually are, so why not? and its damage, not crits, so while it could be leathal, it won't mean every grenade is an autokill (I think).