Haven't camped at Big Meadows yet, but from what I've heard, a mid-week arrival without reservations might work - it's a pretty large park, and the lack of hookups limits its appeal for some. For me, it'd depend on what time I was arriving. I'd do it if I was arriving by early or mid-afternoon; maybe not if I was planning on pulling in at dinner time. Can't be sure, but worst case scenario might be having to move from one site to another during your stay. That wouldn't bother me, but I'm in a Class B.
Weekends in the fall foliage season are really packed up there, but I'm under the impression that the rest of the year isn't that bad.
