I would start by trimming the holly trees topiary style. The small plants in the front seem out of place with the older more mature landscaping.

Thanks everyone for taking the time to comment. This is my first "discussion", so I apologize for not including the basics like USDA zone! ;-)
We live near greenville sc, which is zone 7B. The house looks to the northwest so the sun travels the length of the house throughout the day. The driveway is a horshoe, and there's a large island of trees in front of the house which makes a straight on picture difficult. The front area that you see gets about 6 hours of full sun.
The biggest reason i've posted this discussion is b/c of the tall hollies on either side. They've gotten so tall that it makes trimming them a challenge. Would cutting them to 8" feet (below the roofline) make them look out of scale?
The shrubbery on the sides is 6 feet tall, and unlike boxwoods that grow slowly, needs to be trimmed once a month. I thought of replacing with boxwoods and keeping them shorter.
The small boxwoods in front are the beginnings of a knot garden and i've added nandina firepower, and trained roses on the brickwork for color.

I'd like to bring the planting farther out from the house by layering other plants in front, but am not sure what would look good....

Try the HGTV plant finder tool. You can enter your USDA zone, the type of plant you want (shrub, tree, annual, perennial, etc.), the type of light, and moisture levels. You will can get back thousands of pictures, which may be overwhelming, but you may get an idea of things you like.

You may want to hire a landscape designer, but in my decidedly unprofessional opinion, I'd rip it all all out and
think about putting in some dogwoods and perhaps some hydrangea and other flowering plants (lavender? roses?). Would you like a varied palette, or a monochromatic one (i.e. whites or yellows)? Some grasses? English garden-style? Native plants?

You have a lovely home. People may blast me, but I'm a firm believer in taking plants out when necessary. One holly appears to be getting more light than the other, leaving one looking thin. If this is correct, even drastic trimming will not help the situation. I'd be inclined to rake them both out, but would consult with at least a reputable garden center, if not landscape architect.

Take, not rake ... Sorry

Sometimes a few changes are all that is needed. I suggest starting with the center and front and allow the back bushes to remain as a backdrop of needed greenery.

I am a landscape designer, and think that you are correct: the plant material is too large and needs constant expensive and time-consuming maintenance. You may be spending more time maintaining your landscape than enjoying it. Six hours of sunlight a day is significant. This means flowering plants will do well here, you need color, texture and interest! You seem interested in exploring options so in addition to the salient points listed above, I would add:
1. What is your style? Are you formal or informal? FIND YOUR STYLE! Start an idea book of landscapes that you like on Houzz.com.
2. Do you want to 'fit in' with the rest of the neighborhood, or perhaps do what you think suits you and your sense of style.
3. I will always encourage you to work with a professional landscape designer, they know how to help scale the landscape and use plants that fit in the space you have when they are mature. APLD.org has some wonderful designers in your area, you can do a designer search on their website and see examples of their work.
4. If you do not use a professional, then I would do what a professional would do: Measure your residence, driveway and existing plants and get this on paper in a scaled drawing, in plan view, for example 1"=8'. This will allow you to see where you need to make changes.
5. If you are like most people, you want a terrific landscape but do not want to spend all your time working in the yard. This may steer you toward plants that give high impact, think color and texture, and at least a high percentage of plants that look good year around. Using a high percentage of native plants are a must in the Tucson, AZ desert where I practice as a designer. You may want to look into this in your area. Many times this translates into plants that are lower maintenance with lower water use that are better for the environment. They may also attract birds and butterflies, something my clients love about the landscapes that I design for them.
6.If you design this yourself, the plant material will need to fit into the landscape when it is mature. I suggest that you work off a plan, invest the time to research how big the plants that you like get. The biggest mistake that I see is not planning for the eventual size of plant material in the landscape.
7. Consider views from inside and outside the house, and what it looks like driving up.
8.Pots at the entry with colorful flowers would look inviting, and spark up the green blob for now and can stay as you work on your project.
9. A well-designed landscape is one of the best feelings in the world! I am in Tucson, Az, Landscape Design West, LLC, if you need more help with questions. Good luck with your project.

This picture reminds me of the landscape of my home when we first moved in. We ripped it ALL out and started from scratch! We added a retaining wall of red landscaping bricks. Then we replaced the big, obnoxious boxy green hedges with great big hostas and lilies. And in front of those we planted a bunch of creeping phlox that have filled in beautifully and hang over the retaining bricks. It's now 14 years later, and I still think it's one of the wisest decisions we've made with the property. We get so many compliments from people passing by!