Quick comment about those people who are on the "feedback is valueable, one shouldn't have to pay, and actually ANYONE should be able to give feedback"-wagon:
You're forgetting something - regardless of if the group of those who can give feedback is "closed" or "open", a lot of feedback is sub-par quality, and it takes effort and energy (DEV-TIME!) to process feedback.
So, feedback always has a cost for the developers (processing).... feedback becomes useful and valueable, when the benefit of the feedback weights higher than the cost of processing it.
In theory, the ideal feedback-group would be closed and magically only consist of people giving at minimum average quality feedback.
Of course, this "magic" doesn't exist in practice. In practice, you don't know ahead of time, if some stranger will be a good alpha-tester. So you're in a dilemma: If you give more people access to the tester-team, you may get more useful testers, or not.... but the effort of processing feedback also will go up.
The "paid"-thingie is a double-edged sword.... ignoring business consideration, it DOES tend to reduce people who just want to play for free, and not return anything..... it however - as others mentioned - will also exclude some possible useful testers, who just do not want, or are not able, to pay.
At this point, i semi-agree with what someone else said earlier: IV should give anyone who in the past proved to be useful testers, free access. Seriously, if quality feedback is your concern, then nothing is more efficient than people of whom you KNOW ALREADY that they'll be useful. Those kinds of people actually are WORTH MONEY... letting them provide useful feedback for free, would actually be like asking them a favour, not "being nice to them".