No. If anything, the opposite will be true. When soft-proofing for press printing it's most common to have to dull some very vivid colours of the RGB file to fit into the CMKY gamut. (In fact, this is true for RGB printing as well - did you see this thread?)
No, definitely not. (As long as the soft-proofing and related adjustments are done properly, of course.) The balance will be fine. It's just that some colours might be a little duller by necessity.
Yes, it wouldn't be too much trouble at all to put this simple extra step into your workflow, if you felt it was necessary.
But heck, I wouldn't bother. For the small percentage of photos that would be affected, it's not worth it.
Alas, yes.
Again, though, it's only for a small percentage of images (ones with very vivid colours, eg flowers.)
Not exactly. You would only have one file - the PSD file - with a specific Hue/Saturation layer for each print shop, which you applied in accordance with that shop's soft-proofing profile. Then for each print job you'd turn on the necessary layer, and turn the others off.
(In case I haven't already mentioned this, the photos you put in the InDesign document are always PSD files. Never jpegs.)
I agree. It would be wise to do a bit of testing to make sure you had a good system in place, but yes, it sure would save a lot of work.
Is this something you're going to be dealing with a lot? Printing the same images at various print places?