Those are some gaps. Trouble with caulk (colored or not) is what will the cedar siding color be in the future? If you go natural, then one color. If you stain it, another. Personally, I'd put new boards on and then decide on caulk color. If the gaps are smaller, so will the likelihood of the caulk color being an issue.
A forum community dedicated to Do it yourself-ers and home improvement enthusiasts. Come join the discussion about tools, projects, builds, styles, scales, reviews, accessories, classifieds, and more! Helping You to Do It Yourself!