I see people say "wait for the warranty to be up" all the time, I don't really get it. Car will be 100K miles worth of used up by then, and it's almost certainly years in your future. Plus, the tune (well, the Trifecta tune anyway, dunno about others) has a transparency mode that has been tested by a dealer that knew it was there and still couldn't find it, plus any tune can be flashed back to stock if you're that paranoid, and finally some (not all) service departments won't void your warranty based on this or other mods if you talk to them in advance about them; you could try that latter idea out on a nearby but out of town Chevy dealership so if they reject you it's no big deal.
It's just me, I know, but I'd say get the tune, the difference between tuned and untuned Sonic is night and day, and there's little real reason to worry about it wrecking your warranty.
I'm not one to talk though, because I can assure you with my list of mods, my own Warranty isn't worth the paper it was printed on... except that my local service HAS agreed that they will still cover anything that isn't clearly a new part or definitely caused by one. YMMV on that one.