"Restricting" a spell to something narrower than what the guidelines and examples allow does not lower its level - among other things, this would unbalance spontaneous magic: restricting a spontaneous spell to "this one target, this one time" is no restriction at all!
But "restricting" spells can have other benefits, to the point that it's not even clear it can always be done. For example, a spell to turn a pig, and only a pig, purple would tell you whether the target is a pig, even when it would not be otherwise apparent, even without using Intellego. This has been discussed at some length here.