Since you are curving your plates to achieve a target press response then the color bar should be curved.
(the issue about the value of what the color bar tells you is debatable)
From a press operator’s point of view the only color bar elements that they care about are the solid ink patches. That’s why many color bars just have solid patches.
I know many press operators who would disagree with that statement.
Screened patches of known values are nice to use when determining dot gain.
From an operator’s perspective, absolutely. Trapping, doubling, and slur targets are just a few of the patches that are convenient to have. One of those being extremely useful over any of the others. It’s all just personal preference, of course, and isn’t completely necessary. But then again, neither is a curved color bar.