One doesn't have to be a great gardener to have a great garden.
In your wandering and observations all of you have come upon great gardens.
I divide great gardens into two groups; those that were bought and those that were built. Make no mistake, a great garden can be bought. There are a handful of truly amazing landscape designers and contractors here in Southern California who, with the proper amount of resources, can serve up not just a good garden, but a world-class garden.
Likewise, all of you have seen great gardens that were more labors of love than the product of a hefty checkbook, these were created by a rare devotion to the garden combined with almost constant adjustments and tinkering.
Lots of money certainly doesn't equate to a great garden any more than lots of love and tinkering does. But occasionally, truly superb gardens can arise from either approach.