Unfortunately, not all spells should be mass spells. The trick is effectively limiting which spells can be meta'd, which you've tried to do based on ranges. Most proposed metamagic feats have this problem, because as the books with new spells in them multiply, new spells may not be compatible (balance-wise) with the metamagic feat.
What you probably should do (and I, personally, would dread doing myself) is look at all of the Touch, Close, Medium, and Long range spells in the books you'll be using for the campaign this house rule is entended to be used in. Think through how each spell could be abused by being made a "Mass" spell. If nothing is game-breaking, then you've got a feat that works for your campaign.
That's alot of work, though. Good luck?