Very interesting idea this, I admit I rather like it. Goes a fair way towards making grenade weapons worth having, always bugged me too, the way they just cease to get better. One point for clarification though:

Quote Originally Posted by Forged Fury View Post
...you can immediately make an additional attack against any creature adjacent to the first using the same attack bonus.
You might wish to mention what happens with something like true strike, I doubt you want someone giving themselves 5 attacks at +25, at 3rd level do you?