Just a few thougts:
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Flush vs change: Flushes of all kinds (except coolant and brakes) are usually designed mostly to increase profits. However this is not to say they do have some value. There does not seem to be well defined meaning to either term these days.
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A standard transmission flush does not get the filter change. I believe it is very wise to make sure the filter gets changed. A standard fluid change should include a filter replacement.
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A fluid change does not change all the fluid. Of course neither does a flush, but the flush does change more.
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A flush or a change will not damage the transmission. However it is true many transmissions fail after one. The reason that the transmission was failing and the change or flush was done in an attempt to fix the damage and it was just done too late.
It is not easy to determine when it is too late for the fluid change or flush is too late, but overall in a situation like your where it has not yet begun to miss-shift I would suggest that a change or flush (I really suggest you make sure they change the filter) is well worth the cost.
Depending on the situation it may pay to have a second fluid and filter change a few months later.