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It should not make a noticeable difference in ride, handling or noises. A lot has to do with the tires you choose to use rather than from 17" to 18". So choose your tires wisely, good luck...
As stated, tires are VERY important, but also choose your wheels wisely. Poorly matched offsets and/or heavy wheels can destroy the on-road feel of the car as much as poorly selected tires.
Also, depending on how much the overall rolling diameter changes (wheel and tire), it may offset your speedometer reading. If you're keeping the same rolling diameter when going from 17" to 18", you will have to decrease side profile on the tire, then there will be a noticeable decrease in ride quality, it will be bumpier, but may handle slightly better due to less sidewall flex.
It all depends what you're looking for, if it is for appearance, then most likely you will go with a smaller sidewall at the cost of ride quality. If you think that ride quality is more important (considering it is for an LS430), then you should go with a 50 profile at least.