Ive brought dogs to the er/vet in panik of their life or that it was serious. Most the time as you said, it resolved before the vet could even see the dog, or it wasnt as bad by the time i arrived. So now I stop and think about it, and wait a bit to see if they get better. Of course if the dog was not breathing right as your dog was, I would def take him or her in. But something like diareah or itchy skin, I can take care of at home mostly.
The vet is almost an hour away from me, so I can see how it could be easy to just go to the vet if you are only a few minutes. I would so so love to be near a vet! Maybe if another situation arises, assess the situation a little longer and think to yourself, "is this something that cant wait til the morning?" or do a google search for at home remedies or over the counter meds that you can remedy yourself. For example, try a soothing oatmeal bath or start her on a suppliment to improve her skin and health if you havent already. Google is an awesome tool! lol
But there are obvious emergencies so please dont wait for your dog to "get better" I have seen posts on other forums where people ask for advice in a situation where clearly the dog should be rushed to the er.
Dog Owner's Guide: Is it an emergency?
Hope I helped, vet bills can add up quickly!