Part of the reason that I support a 1500TT into the 121 world is because at 500TT you want to fly. You still see it as a privilege to be allowed to fly at all. At 1000hrs a year, you have 6mos experience. At 1500TT you're beginning to realize that flying is just a job, albeit a complex job, with diverse and important responsibilities, but really, its just a job. You may find satisfaction in it, you may find purpose in it (I find some) but really, first and foremost flying is just work.
That's the change in reality (or at least it was for me, at about 1000TT) that though this is fun, I'm an employee, and I'm not willing to take crap wages just so I can fly. I'm not willing to suffer so that they can "do me the favor" of letting me split legs and throw the gear lever. That's what's important in my opinion. We wonder why guys take these jobs. Really, in terms of coolness, longevity, and the ability to build your career, it makes sense to jump into the right seat at 250TT, that being said, I'd recommend against it, because when I went into the right seat at 500TT, flying was still inseperable from the hobby that I had started out in, and not yet a career. There's a difference in mindset that doesn't go away for at least a thousand hours. I still love to fly, I still love my job, but I definitely no longer consider it a privilege to be able to work for someone, especially if I was to be paid far less than my counterparts in other parts of the industry.