So skiing fast would your advice be to go the week of the opening if we want to go on these attractions? Do you think the lines of the other attractions will be about the same in both weeks if they don't soft open Cars or the Matterhorn?
I'm not sure what you mean about "same in both weeks".
While soft opening may help, probably only if they are really a pre official opening not a regular soft opening. Like Carmatts said a soft opening will be unnanounced and only a few hours long. While I agree once open it will be all over twittter and people will show up, but that doesn't mean it will still be open. For soft openings to help these attractions will have to be open most of a day for several days including weekends to let a lot of people ride so they don't feel the need to go when it officially opens.
Look at last year.
Little Mermaid was open on and off for a week, then on opening day it had a 4 hour plus line that over flowed it's queue and was in the whole of Paradise Park, which fits 4,000 viewers for WoC in just the viewing spots not the access spots. In a day the wait was down to an hour, and within a week settled into 20-30 minutes long at worst for the rest of summer. What helped Little Mermaid relax quickly was it has high rider capacity and not a E-ticket.
Star Tours was also open for a while, and had an AP preview. Then when it officially opened, FP was distributed in an hour and the line was several hours long wrapping its way down to the end of Main Street and back and all over the hub. Star Tours then fell to multihour waits, much better than several but still really long. FP would go in a couple then a few hours. It was a popular E-Ticket with only good capacity.
This year it's likely that if they don't have huge soft openings, and by this I mean allowing 10,000 riders per days on 10 or 15 days it won't help.
On opening day expect a line at the DCA gates of 10,000 people, that go strait to RSR. In the park RSR appears to have a long queue and decent overflow queue set up, think of it as like Indiana Jones. While this should work fine mid summer with luck or at least by the fall, in the opening day and perhaps a couple months I think the queue is going to go down the crossroad in the warf area. While opening day will be crazy the line may still die down to a long 3 or 4 hour wait. RSR is looking to be a super great E-ticket attraction, think Indiana Jones or Splash Mountain, very nice without great capacity. FP will probably be like ST gone in an hour or a few hours.
LFT and MJJ have a bigger problem, low capacity. So while not nearly as popular there lines will be slow. Maters Junkyard Jamboree has ok ride capcity because it has two ride systems, it's a side by side attraction. So set 1 and set 2 should load alright, moving the line better. Lugi's Flying Tires will probably load awful. We've all been on bumbper cars, it takes a while for people to get to the last open car and then to check the seatbelts in the randomly placed vehicles. In just some speculation this attraction may have a very novel loading sytem, but I have seen no direct evidence that it will. With low capacities and not being great attractions, it's kind of a mix of what will happen. They will probably never have a under 30 minute wait all Summer and it may take a while to knock the wait to under an hour.