my suggestion is to use the beta world to test new changes. this would give the population of highly involved users confidence in your changes. also, it would give a world of credibility (pun intended) to your commitment to putting out a quality product, by investing in the test cycle. and it would serve to make the community feel like you really cared about what they think, and are committed to working with the community to make the changes that are best for the game. you probably get more bang in a PR sense than you do from the testing standpoint, but both would be very significant. i would quickly run through like 5 recruitings to give people decent teams, and then just run 1 season with new engine changes with those users, and then reset the teams.
also, this would give you a chance to hash it out with beta users in the beta forum, keeping much complaining and questioning off the main forums. if you can convince the most highly involved users before the change goes live that its a solid change, well tested, then you will absolutely experience much less resistance and negativity when you release the change. if you've already won over the most vocal users, then instead of having the most vocal users questioning your change, you would have them supporting your change, and that would do wonders for the morale on the main board in response to new patches.
thanks for your time!