If the fact that you have a Valentine's date isn't enough to cement your reputation as a consummate lady-killer, perhaps wearing this outfit is.
In the absence of grand gestures, like a bunch of roses bigger than your body or a diamond-encrusted-something, being well turned out reinforces the idea in your Valentine's head that they're still well worth the effort of getting dressed up for. In turn, this probably makes them feel just as warm and fuzzy as if you'd spent the money on a gift instead.
But that doesn't mean you have to turn up suited and booted. In fact, the best approach is to keep things cool and casual with a nice shirt, a touchable borg-collared jacket and some decent boots.
Now, don't you feel less guilty about splurging on some fresh new threads? A treat for you is a treat for them.