80% of my Camino is in June, so I’m not in the spring/rainy period. But how to be ready and not carry unnecessary weight...that’s the question. REI and Eddie Bauer both have packable rain jackets on sale, so we’ll see. I have a cover for my pack already. Since most of my hiking has been day hikes in the last 10 years, I’ve been acquiring new/different gear and quick dry clothes for the Camino. And now, I’m near the end of that budget. Hmmm.
A poncho, which I prefer, is lightweight, extremely well ventilated, and will also cover your pack, so no pack cover is necessary. In breezy or windy conditions it can be belted. My rain gear consists of an ultralight poncho, a rain kilt (if the rain is chilly, otherwise it's just bare legs under the poncho as I only hike in shorts). Total weight ... 9 ounces.
Frogg Toggs are lightweight and less expensive than most rain jacket/ pants. They are light but they are less durable than most other more expensive options. Since you are not doing any bushwhacking while walking Camino, that won't be much of an issue.
https://www.froggtoggsraingear.com/Hiking.shtm
In REI's inventory, the Marmot Precip jacket and the Outdoor Research (OR) Helium II are good choices, they have pants as well. They will be in the neighborhood of 9 to 11 ounces for the jackets. And, depending on how active and how much you perspire, you may face issues of getting wet from sweating.
For Camino, if I were going with a rain jacket configuration, I would go with Frogg Toggs/DriDucks for the economy and the fact that they are actually very breathable for a rain gear.
I would also use a waterproof liner for my backpack and not use a pack cover. Even if using a pack cover I would use a bag liner or water proof stuff bags, as water can penetrated around the cover and wet the bag itself during heavy or prolonged showers.