I think it depends on a lot of things, including the breed. For example, a laid-back Newfie is pretty darn laid back, but a laid back Parson Russell is still pretty active. So what is typical for the breed? You’re looking at Welsh Springers, right? I’ve only known one, but if they are similar to English Springers, then even a laid back one should be fine for your purposes. I would think most dogs would be up for the types of things you mentioned, even if they to tend towards the laid back side.
I know what you mean about not wanting a dumb puppy, but the best way to avoid that is to make sure the parents have brains. And it is very possible to achieve breed championships without them (not to say that you can’t have dogs that are smart AND good looking, just that having a CH or even GCH is no guarantee). Does the breeder do any sort of performance things with her dogs which might be a better test? Have you met either parent and been able to get a sense from them? It can sometimes be hard to tell by watching them as young puppies. Cookie for example, used to fall asleep in the litter box (and other things that made us wonder) but as I’ve discovered while working her in Obedience she is actually a genius. Reminds me of an absent-minded professor sometimes.