For printing, the smaller 300 dpi file will normally do as much as the larger 400 dpi file will do, simply because this color print did not contain more detail itself. But there are other valid opinions, not about the detail, but about the upsampling. You may like the 400 dpi image better than the 2X resampled 200 dpi image for reasons other than detail. Upsampling the 200 dpi image to be 2X larger above caused its jaggies to be more visible. Images at 200 dpi and then scaled 2X larger do have more jaggies than if scanned at 400 dpi.
Video screens show every image pixel directly, where printers normally show a more averaged view.
Therefore, my previous suggestion was, if we need to scan color prints for large images for printing, then scan at 300 dpi and hope it helps somehow. It can help some, and it will remove any uneasiness that more scan resolution might help, and will add the warm fuzzy feeling that we have done all we can. If you specifically want a large image, there's nothing wrong with scanning at 600 dpi, unless memory or disk space is a problem. But if a problem, scanning color prints at 300 dpi will be as effective. For printing purposes, scanning color prints above 300 dpi won't help much, but won't hurt either.