We were in Norway last August (for a cruise) and the weather was mild and pleasant, but we did have light rain a day or two. We've stuck to Spain in the Fall (Sept-Oct and Oct-Nov) and the weather both times was pleasant - but it was still warmer than I remember Norway ever being.
To my thinking, Norway (pretty much any northerly destination) is my focus for Summer travel. We generally are Spring or Fall European travelers, so catch the shoulder weather in most destinations - good and bad. I think the more Southern parts (Greece, Southern Italy, Spain, Southern France, etc) are really good for sun lovers who want the heat, but for me, if I had to travel in August, I'm likely aiming for all the lovely Northern options - from Iceland, the British Isles, BeNeLux, Germany, Scandinavia, or the mountainous areas in places like Italy, Slovenia, France, and Spain.
- Weather (too hot? too rainy?) - I recommend Norway unless you're looking for a tan and lovely beaches.
- Prices (accommodation, transport, meals) - Spain is way less expensive overall, and I find Spain to be one of my favorite "foodie" places anywhere.
- Crowds/tourists - Spain will be more crowded by numbers, but it is HIGH season in Norway. Still, Norway is PERFECT for Summer.
- Overall travel experience for a first-time visitor - I wrongly avoided Spain for many years (stupid me) and found it to be insanely easy to enjoy as a first time (but seasoned) traveler. Norway was pretty darn easy, but the biggest gap I found was pre-travel information. For every post here (or elsewhere) about Norway, there are a dozen(s?) about Spain. If you're a "pre-planner", Spain is super easy.
Long story short, Spain and Norway are both worth your time and money. Since August is the month you've got, I say Norway is the better option. Maybe your next trip can be in the Spring or Fall and can be Spain.