If you buy a sandy soil and dump it on top of a sandy soil that's kind of redundant. I got really good results with ordering pit run from a gravel yard and dumping it on the ground here. Just about everything I tried grew great. However, you are assuming when doing this that the part of the pit they bring you has a good mixture of soil particle sizes and not too many rocks.

If there is enough soil already on the place to make raised beds with it maybe all you need to do to get good results from plantings is to mulch and fertilize as needed. Otherwise what kind of mix to buy is a matter of what kinds of plants you want to cultivate. Do keep in mind that "manufactured" soils that dominate supply here are artificial mixes just as are potting mediums used in container production. At one point one major supplier here was even incorporating construction debris into its "soil" products (and probably still is). It is preferable to use actual natural soil whenever possible.

It is often practical and most efficient to import a soil mix to raise planting areas. I've worked with most of the local soil mixes at one time or another and have found them all to be perfectly adequate in that they have a range of particle size necessary for good drainage and enough organic matter to help with moisture retention and to stimulate soil organisms. The drawback of any of these is a propensity for some to be weedy - I've had much better luck with Pacific Topsoils and a couple of other private distributors as opposed to Cedar Grove in this regard, but I haven't used Cedar Grove for sometime and they may have gotten better.

A 16" depth is more than adequate for perennials and even most shrubs and any further root penetration will only serve to eventually comingle the imported soil with the indigenous soil. Any mix that has a fair amount of organic matter (compost) in it will be of benefit to the perennials, so go with what you prefer and what the budget allows. Remember that organic matter will continue to decompose and so disappear over time and will need to be replaced in the form of a regular mulch or topdressing.

>I've worked with most of the local soil mixes at one time or another and have found them all to be perfectly adequate in that they have a range of particle size necessary for good drainageEver put some in a jar with water, shaken it and seen what settles out?

I have.