I've never really been in a situation when playing a sorcerer where heightening a spell would be better than just using a spell of that level.
It's rare, but with a Sorcerer's limited spells known, it can happen. For instance, let's assume you've just hit 14th level and got your first 7th level spell. Arcane Spellsurge is it, if you know what you're doing. I'm assuming you've got a Runestaff for Elemental Body. That 3 spells per day (and let's assume 1 more from CHA, shall we?), one going to EB, you've got 3 left. Now, I'm not sure you'll be casting this 3 times a day. Probably, but who knows? Well, actually, I'm sure you will.
Now look at your 8th level spell when you're 16th. It's what? Greater Arcane Fusion, right? But what if your only Will Targeting spell is Freezing Glance? Won't you agree that +2 DC is worth a higher slot for this spell? Or you're fighting a Black Ethergaunt, and know that without Heighten it does nothing? Perhaps you want +4 DC for Wings of Flurry? I'd still prefer GAF.
I agree it doesn't come up as much, but what with your fairly limited spell choices it might come in handy. It's one of the better Metamagics for DC based spells (...wait, isn't it just better to make the spell itself better with Metamagic?). I'd still prefer other Metamagic most of the time, such as making that Wings of Flurry Maximized, though.
You know what, after all that looking at options and spells, I've decided I really prefer other Metamagic. Also, Sorcerers are all the more pathetic now that I've looked at the table again. Hell, without Metamagic, I could predict their every action. Still can, probably. Good thing my DM is reasonable.
Heighten gets an F.