There exists a pretty large group of people who aren't bleeding edge raiders, top of the ladder pvpers or diehard theorycrafters, but who still take a keen interest in what happens to their class and what other players have to say. Much more so than a casual player who learns on their own or from/with a small circle of friends at their own pace.
That group can be further classified on how that information is used. At one extreme you have the flavor of the month folks who change their entire play style around the newest bit of intel available and on the other people more like myself who are not going to change something that they enjoy to benefit from a buff or escape a nerf.
A prime example is my hunter, I rolled marksman when it wasn't the ideal spec; beastmastery reigned supreme throughout BC. As I was leveling I picked talents that complimented my play style and as it turns out they were mostly in the marksman tree. I remember back when WotLK had recently come out and survival was the "best" spec I was in the inn over in one of the Northrend starting areas and a mage came up and whispered to me something like, "you know survival is better right?". I don't recall what I said to that if anything, but if I did I am sure it wasn't nice. :)
I was also a feral druid/dps hybrid since I made my druid and still am to this day. Even with dual specs I took Resto as a secondary rather than min/max two specs for feral DPS and tanking. I've always leaned on the tanking side when speccing, but I do forgo some of the less vital tanking talents to be more proficient in my kitty gear. I am sure I could do more dps if I specced exclusively for it, but as is I know my class well enough that I can put out competative damage plus have the added utility to tank or heal at a moments notice. That is what being a druid has always been for me.
None of that has anything to do with any research into what others have discovered about my class though. That information does play a part though, just a pretty small one. The most valuable source of information in that regard is Blizzard themselves. When I change something it is because of a fundamental change in the class, like the talent trees were redone or a new ability was added. I don't ever have to worry about a small nerf here or a buff there. The little stuff handles itself if you follow the developers vision of the class/spec.
Fighting your class/spec does have short term benefits, but those come at a cost. The trick is to figure out what blizzards plans are for your character and use that as a guideline. There are things out there like diseaseless dps for death knights, add-ons that automatically cancel eclipse procs to benefit boomkins, stacking of armor penetration above all else for a competative edge. None of these things will last long since they were never intended. Short term you've got yourself something great, long term you will get hit down with the nerf bat something fierce.
I think a large part of anticipating class changes is enjoying the class you play and finding the class you enjoy most is a very time consuming process. Different classes have different feels to them in different level brackets and even then you can't really be sure until you've played it a while. I tend to favor melee DPS and tanking, healing feels like whack-a-mole and ranged DPS just seems to go at a slower pace than melee. I still enjoy healing and ranged DPS, they are kind of relaxing and require a lot less concentration on my part. On the downside they get really boring after a while. Took me the better part of a year to figure that out.
Even within my preferred roles of tanking and melee DPS I still can't get into paladins or warriors, they are too simplistic for my liking at least at the levels I've played at. My warrior is only level 6 and my paladin 23. I know warriors get more cool stuff, but paladins I am not so sure. I plan on leveling a goblin warrior next expansion along with a worgen priest, so we'll see if that changes my opinion any when the time comes.