pain meds are essential for quicker healing. Without them, the dog cannot rest and heal as quickly.
The thinking on pain meds has changed- vets used to tell us not to give them, because then the dog would "move around too much". Pain studies tell us that animals will do what they have to do- they will move to get water and food, and will try as best they can to appear outwardly normal, but if they over do it, they will feel it just like we would.
The pain meds he'll get will enable him to be comfortable, they won't immobilize him or numb the sore area. Animals have an instinct to appear normal, regardless of pain or injury- this is more pronounced in prey species, but dogs are much the same. Their instinct is to not stand out from the pack as the weak one. With or without pain meds they feel like they should act normal. So they might as well put all their body's strength into healing, rather than dealing with pain and it's affects on the body and healing. The ace will sedate him, but the aspirin will help ease the pain so he can rest.
Sorry, this is a soapbox for me. Our pets no longer have to endure pain following surgical procedures or injuries. They can be comfortable and be able to rest without constant pain (that they would never let us know they are feeling).

It sounds like he's doing better, I hope he continues to improve.

I've had a couple of dogs that had spinal injuries- one had alpha stim treatments and underwater treadmill therapy, but both recovered- one fully and the other just some incoordination remaining. Neither had surgery.
vickie