You want the opinion of someone younger? Here it is...
I was raised to love the Camaro and hate the Mustang (and all things Ford). I grew up looking at pictures of Camaros that my dad owned and eventually had to give up to raise my sister and I. I absolutely loved everything to do with the Camaro and felt disgusted when someone even thought to say that the Mustang was better. My first car was a Camaro and, before that even, I joined C&G searching for 5th Gen Camaro pictures. I joined after seeing Walt's chop of a black 4th Gen into what he expected to see out of a 5th Gen.
With the minor exception of '82 (and a few years of I6s), Camaros have always been V6 and V8 only. However, the world is changing. If you can think of one modern car that is pure muscle with no refinement, what do you think of? That, my friends, is the Viper. How have Viper sales been? Poor. So what is Chrysler now doing? Giving it some refinement and coming out with something much more polished than ever before. If even the Viper has to change to accomodate refinement and more efficient packaging, why should the Corvette or Camaro have the privilege to stay the same and not evolve whatsoever? They don't have the privilege and they never will because the only thing that is constant is change, which is ultimately very true for the auto industry.
That being said, the Mustang's latest MCE is exactly what GM is missing. We were told by GM that we were getting an amazing car that would be nearly perfect in every aspect with the 5th Gen Camaro and, on paper, it mostly was. We received a very good exterior design, much better suspension, sufficient engine choices, and more technology than a Camaro has ever seen. With that we also received nearly two tons, a hard plastic dash, and a rather large feeling car. When I sit inside a car, I want something that Cadillac is striving for: "When you turn your car on, does it return the favor?" With the Camaro, it does not. Sure, it was fun to slide a 2SS around some corners and bring it up to 120 on a back country road, but there was something lacking. To me, that something was that it felt large and acted as if it needed all of its 426 ponies to get it going the way it did to push that weight around.
I admit, the car felt large partially because my last two cars have been forced induction four-bangers making around 300 HP with a curbweight of about 1000 lbs less. These two cars feel like they can go all out with little effort whereas the Camaro really needed to be pushed, and my SRT-swapped Neon actually felt quicker than the Camaro (though I can't confirm or deny whether or not it is). I didn't get that special feeling out of the Camaro, though I know GM has the ability to do so. I drove a Corvette Grand Sport about a month later (yes, I know, it's a much more expensive car with a way better suspension, but it is the Camaro's big brother so to speak), and it gave me that feeling from the start. As soon as I sat in the Corvette and felt it just wrap around me, I knew I was in something much more special than the Camaro I had driven. Then I started it and mashed the petal, and that same motor gave me a thrill that I hadn't seen whatsoever in driving the Camaro.
I then test drove a 2011 Mustang a month or so later. I didn't even intend to drive one, but once I sat down in one at the dealership, I knew that I had to. It gave me a much better feel than the Camaro, and I felt more welcome and invited to drive the Mustang. I started it, and drove this V6 Premium model around for a few minutes. There is one word that best describes the Mustang's feel to me over the Camaro's, and that word is tidy. The Mustang just felt tidy. It felt much smaller, lighter, and more nimble than the Camaro. Heck, even the much smaller amount of power in the 3.7L V6 even made me feel better than that of the 6.2L V8 in the Camaro, not because it was more powerful, but because everything about the car felt much more sporty. And this is what these cars are trying to be, deep down they are sports cars, so they must act and feel the part. They are no longer what they used to be, rough racers that are straight-line contenders only. However, they still should embody that spirit and live on as contenders in every aspect that defines a sports car.
As a younger person who could actually afford a Mustang or Camaro, I would choose the current Mustang because it is mostly what these cars need to be as of right now, and that says a lot given my history with these two cars. I've even considering putting down money multiple times to get this car in my driveway.
That being said, the Camaro especially has to get smaller, as GM already realizes. It needs to be more efficiently packaged like I feel the Mustang is. It needs to bring you inside of it and tell you, "I dare you to start me." Whatever happened to having a "bitchin' Camaro" back in the day? That's what we need now, a bitchin' Camaro. If it were to lose the weight necessary and have a tough-sounding I4 turbo with 300 HP, then why not? 300 HP would result in a quick car and, if it is packaged correctly, this engine would give a very respectable fuel economy. I think everybody is offended by four cylinders in this car because it will eventually have a fart can put on it by some little fanboy teenager one day, but turbo-fours tend to sound much better than any N/A four-banger no matter what you do to them and their exhaust and, no matter what happened to the exhaust of such a motor, the sound of it would most likely not disrespect the Camaro name IMHO. Also, if we're already getting 300+ HP out of a mean-sounding I4, then why should we throw a V6 in there? The I4 will be more efficient, possibly lighter, and would be showing its true potential. You don't really need a 350 HP V6 base engine in the car, 300 HP is honestly more than enough, especially if the car is much lighter than the current car.
Will people accept this car though? Maybe not right out of the gate. There will obviously be people snarling about it, but they will still have a V8 option without a doubt, and I don't see that going away for awhile. If the Corvette has a V8 (and it has since the 50s), then the Camaro will as well in some form or fashion. If the base 6th Gen Camaro can almost perform with the 5th Gen SS (as the base 5th Gen nearly can with the 4th Gen SS), then what's the difference in what engine it has? Just build us a car that gives you that 45+ year heritage, sports car spirit, an interior that makes you feel absolutely crazy just sitting in it, the performance (in both power and fuel economy) to outperform anything else in its segment, and call it Camaro. If that doesn't make you happy, no matter the options you're given in the car, then nothing truly will.