I'd suggest that you consider a larger depth deck at the top of bank of the creek, size it at least 8 to 10 feet deep so you can actually put chairs/small coffee table on it and hang out there. Not all of that would need to fully extend out over the slope, you could carry a portion over into the flat part of the yard as well. For obscuring the edges of the paths without having to redo the whole thing, why not consider using ground cover plants to creep over the edges. Simply removing the visually jarring brick would be a good start.

I don't know if you prefer to stick with natives to do this, but some of the low growing natives such as Arctostaphylos uva-ursi, of A. 'Emerald Carpet', Erigeron glaucus cultivars of Zauschneria cultivars would work well.

I'd also suggest that the outside loop of the path against the trees could use a framework of contrasting medium sized shrubs, and things like Arctostaphylos 'Howard McMinn', Mimulus aurantiacus, Ceanothus 'Joyce Coulter', Carpenteria californica 'Elizabeth', Ribes sanguineum v. glutinosum, Rhamnus californicus 'Eve Case', Heteromeles arbutifolia, Salvia clevelandii or various Eriogonum species such as E. grande rubescens or E. giganteum, Galvezia speciosa could look nice. Native grasses to throw in the mix for foliage contrast might include Festuca californica, Eleymus condensatus 'Canyon Prince' or some of the different colored Juncus species.

You didn't ask, but that foreground planting of the ugly winter deciduous hybrid roses absolutely kills the aesthetic potential of a serene winter view into the garden, and I would move the roses to the periphery in sun areas where their barren nakedness wouldn't be so apparent. Can you tell I am not a big fan of roses? If that area is full sun, it could look brilliant with plantings of some native succulents such as Dudleya hassei, D. cymosa, D. pulverulenta, in combination with our native Iris douglasiana or cultivars of various colored Pacific Coast Hybrid Iris or Iris 'Canyon Snow', and perhaps a large succulent accent such as Agave 'Sharkskin' or Dasylirion wheeleri. Other native perennials to consider might include the various Heuchera species and hybrids, Polystichum munitum, Darmera peltata, Sisynchrium species, and Sedum spathulatum 'Cape Blanco'.

If you are not opposed to using some more water loving plants in the redo of the garden, it would visually link the far side of the garden with the orange tones of the fall foliage on your Persimmon tree, if you had some orange foliaged plants such as Libbertia peregrinans or Stipa arundinacea at the far side of the garden fronting the backdrop trees.

If you didn't necessarily want to go the natives approach, I'd suggest you browse the book put out by EBMUD, Plants and Landscapes for Summer-Dry Climates of the San Francisco Bay Region, or the new book by Scott and Lauren Ogden, Plant-Driven Design, Creating Gardens that Honor Plants, Place and Spirit.

You have a fantastic site that offers a lot of potential with the captured view backdrop, take advantage of it to the hilt. You didn't say whether you are dealing with deer, however, so not everything I listed above will do well without fencing them out.