I only speak from experience with other vehicles. Not Toyota and not Scion. But I have a LOT of experience with highly modified high performance newer vehicles and what is most effective with them. In most cases, even with high performance factory tuned vehicles, the OEM tune is very conservative. This is for many valuable reasons. They have designed and tuned the vehicle to be safe and reliable in all of the locations they can imagine they can sell one domestically. There are so many factors that go into how your engine operates that are affected by the environment you operate them in.
First of all is what octane they require/intend you to use in the vehicle. Ours, 87 octane. 87 octane is cheap and effective but not stable under high compression and timing advance situations. So, if you want to trade economy for performance, there is noticable gains that could be seen with a proper tune for high octane fuel option.
With that being said, where do you live (rhetorical)? If you live at sea level, air is more dense and your ECU must compensate for this. A tune that is good for a car on the coast may be volatile to a car in the mountains. Additionally, what are your fuel options. Some places Premium is 93 octane or you can find 95 octane at some gas stations, reasonably priced. In Oklahoma, for example, 91 octane is the standard premium and I dare you to find much different at the pump. I know a lot of people tuning with E85 due to its incredibly high octane. Not really available everywhere. Another factor, in my humble opionion, is "real" gas vs. ethanol enhanced gas that is very common around here.
I could rant for days on possibilities but I do know that I have realized up to 20% HP gains on multiple vehicles with basic bolt-ons and a proper tune for 93 octane pump gas at my particular location and elevation. I can't imagine if there was/is someone willing to invest in the research and development to properly tune our econo-box we could see noticable gains. But what you have to consider is, is there enough PROFIT and MARKET for the big tuners to do this. I don't believe there is. Hence, no major tuners have.
Again, just opinions based on my 20 years of trying to go fast. Until now...