Look at the math again. You can get what, maybe 10K in trade for the Sonic if you're lucky, and everything you're looking at is going to run somewhere over 20K, so you're spending at least 10K to move up. Even if I'm wrong, cut that in half somehow and it's 5K.
Now ask yourself what could you do to the Sonic for 5K? Intake, tune, exhaust, flexfuel conversion, that's under 2K. Leaves you 3K to play around with the suspension, maybe get someone to slip you RS steering programming, think about a turbo swap... and there's still money on the table.
But all of that is really nonsense, because for under $300 you can get a tune that's going to be the biggest single bang for the buck improvement of the whole lot, and you can pocket the other $9700!
Find someone with a tuned Sonic, even if you have to spend a couple hundred bucks on a road trip to get to them plus buy them dinner, you're still looking at significant savings.
That said, I agree that what you really want is a car you really want. For me, that's the Sonic, and I have a lot of fun "improving" it, which I wouldn't have had if I'd bought something already hot out of the box. Yeah, I have a $22K Sonic, when you figure in all the mods, but when I have a certain sense of pride in the car, it isn't because of what I spent, but because I did did some of the work in making it so. If what makes you happy is the Veloster, that could be worth the price.
If though what you're thinking is that changing cars from something you like that would be better with some work to something you like less but that doesn't need any work to perform the way you like, well, no, that's probably not the way to go.