not necessarily. when are you planning on being here? if you are gonna be here on friday you can get vouchers for the whole weekend if you want to go up during the day. after 7pm you dont need a voucher and you can get right on, they dont close the dunes until 930pm.
now if you dont have a voucher, but still want to go up during the day, just find someone in line and ask them to pull you in, (this is legal) 99 times out of 100 they will, unless they are major dicks. most jeepers (especially modified older ones) will help you out. if they are older dudes in brand new/fairly new stock jeeps, chances are those are the dicks. (you know the ones, they wont even waive to you in passing on the road)
other types of vehicles will help out to, it has just been my experience that most jeepers will help other jeepers out.
I might get slammed for this post, but these are just my observations...