I know a few guys who have taught English now for 10+ years. They've got families and houses and are able to get by alright. They are able to supplement their income with side jobs (teaching private lessons, freelance graphic design, translation work, etc), which is a form of career progression. It's true you probably won't get rich teaching English, but it seems like it's possible to enjoy a pretty decent standard of living in Japan on a modest salary. And the fact that you were able to save 50k is proof of that. That's more than lots of people are able to manage - probably enough for a down payment on a house here, in fact.
I saw in a previous comment that you said you are ashamed of being an English teacher. Don't be. You're performing a useful service that people are willing to pay for with their time and money. That's something to be proud of and I would even go so far as to argue that the benefits to society of teaching English are a lot more tangible than a LOT of programming jobs.
Not really trying to steer you in any direction. As I mentioned above, teaching English was not for me - I really hated work environment at the company I was working for. And your concerns about career progression, salary, and status are definitely valid. But on the other hand, I have seen that it's a viable option if you choose to go down that route.