Less is more, or more is better?
An example showing how a simplified, pared down planting scheme with just a few key plants, but planted in mass can really make a border zing. This raised planter between two retaining walls has gone through many different iterations over the years I've been working on the garden. It was full of big bulky Rhododendrons and Abutilons when I first started with the garden redesign. We then transitioned to a mix of overflowing perennials such as South African Arctotis, California native Eriogonum grande rubescens and Mimulus aurantiacus. The super abundance of flowers in a nice blend was perfect, or so I thought. The client wanted to tone it down and tighten it up. So out it all came and in went this mass planting of monochromatic succulents. Less variety of plant types, but certainly many more individual plants. Who says you can't have it both ways?
Here is a link that might be useful: Massed Echeveria elegans on a slope