But since you only need one of the rays to hit to proc sneak attack, doesn't that increase the spells power?
It does. But adding sneak attack to cantrips would also increase cantrips' power, that's kind of the point of this thread. I don't see why higher level spells should be excluded from dealing sneak attack - you are spending a spell slot after all.
If you're saying that Scorching Ray specifically is too powerful with sneak attack, because you get 3+ chances to hit, then eh maybe. But that's jumping ahead a bit in the discussion, unless you're arguing that no leveled spells should allow sneak attack soley because of Scorching Ray. To which I'd bring up the fact that Eldtrich Blast - a cantrip - fires multiple beams at higher levels, and thus we're back to square one. And are either of the above situations really that different than a dual-wielding rogue?