I should have added that we can hypothetically propose infinite outcomes with educated guesses of some of the character traits that we have seen in canon. It doesn't mean that we can give any more weight to the possible outcomes the boys would have turned out given a more normal upbringing. There are too many variables and it really is speculation that becomes a type of fan fiction.
That said, I find Dean to be prettier than your average guy. Assuming that society treated him as better than average looking people are treated, I am betting that Dean's charm would always be reinforced and that most of his possible outcomes involved a talent for manipulating people to his advantage. That's not a moral judgment; we all do it to some extent. Dean would always have been able to talk people into things and make them like him more often than not. This may have meant extra attention from teachers (unconsciously) and easier advancement in work. However, only to a point, which I will explain later. Getting along with people and coordination would have made sense for him to be a member of the baseball team or involved in some athletics in high school. He likes to perform and is good at improv, becoming his different identities of federal marshal for example, and could have even succeeded in his high school theater department.
One of the constrictions of his potential, on the other hand, was a limitation of the skills necessary for continued success in academia. Dean can visualize how to put together a car and take it apart. He can build an EMF device from a walkman. But he is working with the three dimensional pieces and not figuring the mathematical equations behind his activity. We never once see him sketch out his plans or figure the theory behind his gadgets. He obviously has a mechanical aptitude, but science, physics, mathematics? Too theoretical for the way his brain works. Dean could have been an engineer if he had been able to skip the university courses necessary for the degree and just do the actual work. Also, Dean's lack of literary interest, beyond the necessary research for demons, would have self corrected itself if the potential was there, with all the years since Mary's death. I don't believe language arts was part of his inherent potential.
Dean's potential was always going to be a blue collar worker under the best of conditions. Excluding Mary and John hiring a private tutor to work with him every day. Dean is hands on, street smart, not the other kind. Thank goodness, because he probably is alive because of it in his current reality. In a closer to perfect reality, he could have made an honest living and a comfortable one at that.
Now my interpretation of Dean's character is no more accurate than anyone else in the hypothetical scenario of a stable upbringing. We just don't know what butterfly effect would have influenced the outcome. However, I do think, given certain constrictions of Dean's potential, it is possible to make educated guesses with some clues from the past two seasons. Dean isn't a scholar and more than likely never would be one without extremely extenuating circumstances.
Sam on the other hand, was naturally quick in the way that is measured in school. No matter what was going on in his personal life, the academic road was easier for him. He would have been white collar, and the only thing keeping him from that life is, as others have said, love and family and loyalty. He isn't quite as pretty as his brother (and often hears how wonderful his brother is) although, Sam is absolutely adorable by real world standards. He would always have had to put more effort into success than Dean no matter what the outside environment. His drive and commitment therefore are probably part of the inherent component of his character. Being the second born, I agree that he would be trying to catch up to his older brother Dean. Whether that was a friendly rivalry or one of resentment would depend on too many variables. I see Sam as Richie Cunningham and Dean is the (continued...)