That's good news about your dog's acl getting better
Most dogs have some intelligence but most people don't make their dogs think. Chloe was also primarily kelpie and they are one of the smartest dogs in the world. All working dogs are smart but kelpies are in my opinion the smartest breed. Papillons are smart too (not as smart as a kelpie) but people use them as a toy dog and don't make them think. If a dog has to think about things it helps them become a little brighter than the average dog.
Hide and seek is a good way to make dogs think. They either look for you with their eyes, listen with their ears, or use their nose to sniff you out. It's similar to what they did in the wild before domestication and relates to them looking for food. They have to listen, look and smell and try to find their prey. Dogs are also masters at reading body language and facial expressions. It's one of the ways they communicate in a pack and it takes practice for them to learn.
Exposing dogs to different things also helps. I took my dogs everywhere and they were exposed to traffic while walking along a footpath, big lizards when out in the bush, shopping centres with lots of strange people, the beach and rivers, and the dog park, which they went to every day at the same time for their routine and to play with their friends. The more exposure dogs have to different things that are positive and good, the more they learn and the better socialised they become.