Does a QA tester position open any future career opportunities?

Yes it does help. Professionally, personally, socially.

First, really get it into your head that the game industry is the entertainment industry (think of the classic Hollywood, TV schmoozing and vouching for others, but in a good way), and that means social networking is one of the most important and ongoing tasks throughout your career. I can tell you that many, many positions I have seen filled or heard about being filled were because someone on the hiring company had worked with that person and could say that "they're okay as a human."
So, being physically around Devs is inherently a professional gain, even if you are a social wallflower.
Also, your chances of getting a small quip of mentoring here or an admonishment of advice there, directly from a Dev, goes up from zero to... something greater than zero.

QA testing also teaches you one thing that many people who go straight from college and into the industry usually miss out on; which is humility, empathy and self control over what you say. I cannot stress enough how those three things are VITAL to both a newb and the richest, most-powerful CEO.
I am absolutely not saying people who have never worked real jobs (customer service, janitorial... um... newspaper boy?) are deficient in those areas or have any inherent obstacles to those things, but I CAN say that if you need a little wisening up on when to not answer a Dev with harsh words and complete honesty on how the implementation of his game mechanic sucks, or to bite back a retort when someone who is "higher up" than you is super unprofessional and gets all salty on you, or even knowing when to hold back 99 out of 100 of your ideas so that your reputation (the value of the IP that is YOU) looks really good to other Devs.
QA is generally the lowest social power and the most targeted for a little bit of unprofessional dumping, AND also one of the most important jobs in the entire game company. Can you see how that dichotomy could help you grow both professionally & internally?

You also learn how the software works, how engines work, how the daily grind of bug testing works and how the entire project evolves or even switches gears. You learn to think in an organized fashion, to balance current tasks and keep upcoming tasks in your "RAM". And if you're lucky like me, you work in an area with multiple game companies and has Microsoft employment (I have tested 300+ game title in 4 years, huge AAA titles and hundreds of smaller ones, using probably 100+ different debugging systems, I created test passes, managed people, and worked 12 hours a day/ 7 days a week/ 2 months in a row to test Halo 3)

Never turn down work if you are in a position of needing it. Whether that be growth as a Dev, growth as a person (which IS growth as a Dev), or just because the rent needs to be paid and you could possibly make some new social connections.
If you want to do your own thing, and you want to succeed? The ONLY successful people I have seen make indie games that finished and actually sold something were driven enough to have jobs and come home and work on their stuff. I personally know of not a single "Indie" person who eschewed work and was also the personality type to stop being a dreamer. So basically you ARE a person who will make their own indie stuff, or having a job won't matter anyway.

I hope this helps. Good luck!

Gaming QA is rough work, especially in the months leading up to shipping a title. Expect lots of overtime, and expect to be beyond sick of the game you are testing -- maybe even video games in general.

That said, it's possible to move out of QA and into the design department. Several of the designers with whom I have worked followed this path. However, they didn't just "show up." All of them expressed a desire to do more than QA -- and by, "expressed a desire," I mean "did thing over and above the job requirements." Some learned scripting languages to help automate testing -- thereby demonstrating that they could handle scripting jobs within the design department. Others learned the game development tool chain, which meant they could build levels. And so on. You get the idea.

As the other answer suggests, if you are willing to work (very) hard and learn new skills, you can transition out of testing and into other departments.

It depends on what you want to do and where you go for QA. In my career, I started out in QA, went on to design / production, and ended up back in QA because I liked to so much :) It is possible to get in the industry from a QA position, but you really have to have a plan to get out. You are right in that a lot of the jobs are temp positions. This is because most publishers bring in warm bodies for getting things beyond alpha and then the contracts end after gold master. There are a lot of people who get in to QA with the idea of becoming a designer, engineer, or artist in the game industry, so it won't just be you out there. You will need to go above and beyond when it comes to testing. This will be tough because you are expected to put in long hours once things get closer to shipping. Think about what specific job you want in the industry, research that, and think about how QA will benefit that career. Then focus like crazy and develop a plan on using QA as a stepping stone. Good luck!

That's a tough one. My (limited) perspective is that the gaming industry works differently than other software industries. I think they're more likely to use crowd-sourced, contract, and "early adopters" for testing as you've observed. But if you're passionate about participating in QA, plus have a good educational background and aptitude for it, you will succeed - regardless of whether you end up in the gaming industry or not. Although Agile Process has attempted to do away with QA engineers in recent years, I don't see it working out that well. QAs think and operate differently than software developers, and expecting Devs to do QA results in overloaded Devs, underdeveloped testing, and embarrassing misses in the end. From here, I still see QAs alive and doing well :-)