Gardens are ever evolving life forms. They will never look the same as they did the year before. Some plants will look better, some worse, and some won't come back at all - and sometimes - plants move all by themselves (my Lilly of the valley "walked" about 20' from the patch and started a new colony - squirrels are a possible culprit).
If left to their own devices, you'll find that the plants that are more indigenous to your area will thrive and multiple and choke out other plants. The same will hold true for "natural" plants (those that have not been "bred" for color, size, longevity - etc).
We watch our gardens to see what thrives and what needs assistance. We tend to favor plants that will thrive better on their own, even to the point of taking over other plants. We no longer work extra hard to keep plants that need a lot of TLC (I'm done digging up Canna and Gladiola every year and storing them indoors - if they can't survive the Chicago winter then oh well). We dig up and divide or move at least one small area of the garden every year. There are some plants we would love to get rid of (Ferns), and 3 years later just when you think you've succeeded - up they pop again.
We are very fortunate though, we get our plants free of charge being in the horticultural business. We attend trade shows every year and get free stock (usually 1-2 years before they are offered to the public), and we also visit customers in their greenhouses and more often than not they send us home with "stuff". So we've had ample opportunity to see what works, and what doesn't. There are SOOO many plants we would love to be able to keep, and have tried, but they seem to last 2 years and "poof".