On a spiked chain tripping/AoO build against an army, sure, anyone would want to be Large. On a charge build, you probably reach the person anyway. Against smaller numbers of foes, you don't need to threaten in a huge radius. I'm not so sure it's as great as you're saying. It's just distance, not killing power. And if it is good, let people have it (fighters can't have nice things etc.). I will consider moving Large size up to Moderate, but it's really hard to judge.
Meh. It gives you +1 AC and attack and +4 to Hide basically. Trumped enormously by miss chances, touch spells, and invisibility, respectively. If the caster can get down to Fine, now you're adding +7 to AC and attack, which is significant. Tiny isn't so overpowering, though.