Great questions! What constitutes a DL veteran? Doubt I qualify (6 times, 7th in a couple months) but I'll answer anyway.
1. Any rides that lett or right side is better view/experience?(Disneyland Railroad for example? River boat?
No idea. See I guess I'm not a veteran after all!
2. Your must do snack (no cheating and saying Dole Whip)
Turkey leg for sure, though my wife would probably say beignets.
3. Where is your out the way rest spot?( Both Parks?)
DL - agree with mdmost, the stretch between Small World and Matterhorn is usually pretty empty of people, and plenty places to sit in shade.
DCA - Love sitting on the benches between Grizzly River Run and the wilderness area, just love the trees and ambiance. Or, maybe just in the wilderness area itself.
4. Best Bathrooms?
We usually had good luck with the bathrooms at the Red Rose Tavern in Fantasyland, but now with all the traffic between there and Star Wars land, they are probably a lot busier.
5. Favorite Structure? (Ride/restaurant/shop?)
This is a TOUGH question, so many great ones! I think I agree with a couple of posters that Pirates has got to be the best. The front building, the line inside, Blue Bayou, and then once we get out I usually end up buying something at Pieces of Eight, they get me every time. PLEASE be open in June!!
6. Favorite Photo spot , excluding the Castle?
I always love when you get out of the Tiki room, I usually sit/stand on the steps, and take a picture looking out across Adventureland. That's probably my favorite overall land in both parks.
7. At opening…left, straight or right?
It's better to go left... but we always go right, more because it's sentimental.
8. Best Quick service?
We always wait until we get into the waiting area for Tiki room to get our Dole Whips. The line outside is always long, but there usually isn't one on the inside, at least when we've been there (last time was 6 years ago)
9. Best little known “secret”
There are no more secrets in the era of the internet and social media, lol.
10. Ride you wouldn't mind if it closed, ( both parks)
DL - Finding Nemo. Honestly it's a cool ride, and beautiful, and one of my favorite Pixar films, but I'm on the slightly taller side so I find the submarines really uncomfortable, and a bit claustrophobic, so I'm torn to go on it. Takes away that tough decision. It was actually closed last time we went, and I was fine with that.
DCA - Maybe Jumpin Jellyfish? My kids have outgrown it.