Mike,
If you want to come you still have to register and pay $275 a person plus $40(one time only) if you haven't registered with NSXCA already or renewed it for this year.
This is an event that is not being parted out....whether you want to show up to one day of the event or all of it, you still have to pay the registration.
My understanding is that we are going to be at cars and coffee on saturday and that is an event that anyone can attend....but after that get together its back to being in the NSXCA organized stuff.
I hope you try to make it for the whole event if you can. However there is still fri night, sat night and sun for you to make it out in case if you have to work....so it would be still worth it to come in my opinion because most of the main stuff is towards the weekend...fri, sat, sun.
NSXPO is thurs-sun offcially and theres an optional Monday drive for people staying.
Hope that helps.