Personally, I could care less about panels. Especially these days. I remember the touring for E7 and all the actors saying there were reps travelling with them telling them what they could and couldn't say, etc. I get secrecy. But all you'll get is 'so and so was great', 'the shoot was <insert adjective>', "thoughts on the press tour/fans", etc. With the amount of buzz created from the slightest hints, drop a poster, or a teaser and be done with it, it'll get people talking. Run a teaser with music and the date and a quick clip to get the date and thought in people's heads, etc.
In the past, the stuff that got out was not through actors. Script details got leaked way early that turned out to be true, etc.
I liked 7 and did not like 8. Neither means i will or won't like 9. I said after 9 as well that I won't write 8 off forever until i see 9. I wasn't a big ESB fan until after ROTJ because as a 9 year old, it was 2 hours of my heroes getting their butts kicked for 2 hours
My gut feel though is they're trying to get too much from this and not doing it right. The funny thing about secrecy, too, is that they will put out a crap ton of toys come September that WILL have spoilerish information. It goes back to the first of the prequels when they only put out stuff like 6 weeks early. The E1 soundtrack has a track listing you can see in the store on the back of the case, name of one of tracks was something like 'Death of Qui Gonn'. The definition of something you can't do prior to release. But we'll have a full soundtrack and track listing 3 months out, tons of toys, etc, so things WILL be spoiled ahead of time. Likely not big stuff, but much more than i'd prefer to have out as a fan or head of studio frankly.