I don't think there is a clearly defined cutoff point, it is a continuum!
The longer you go the more you enjoy the space but the more restriction is imposed on sites you can get into!
When we sold our last trailer - non AS - I wanted to stay at the same length, 27' as I found it to be a great compromise, big enough for comfort during longer stays but short enough to get into most State / provincial parks with little problem.
When we moved to the AS, unfortunately, we could not find anything less than the Classic 30 (actually 31', bumper to ball) that had the right layout for us.
We don't have much experience with it yet, and I do think our Hnesley will allow us to back up at sharper angles, but even so, I thimk we will now be that much more restricted.
Would be moreso with a 34 footer.
On the other hand, it seems these days that we stay more at commercial parks than State parks, and the extra 4' is very nice to have! no doubt I would like another four feet even more!
On balance, I feel that for us, the extra space is worth the reduction in flexibility vis-a-vis campsites.
We presently have a TV that I think would handle a 34.
Good luck with your decision! I'm sure you'll adapt and enjoy it which ever way you go!
Brian & Connie Mitchell
2005 Classic 30'
Hensley Arrow / Centramatics
2008 GMC Sierra SLT 2500HD,4x4,Crew Cab, Diesel, Leer cap.