It's such a small space with heat radiating off both the house and sidewalk. There's no space for dwarf conifers. Miniature conifers, perhaps, but they tend to be costly and they grow too; and that environment might be too harsh. Not being defeatist, but it seems to be be too small an area to get super creative Keep the weigela if it does well, scrap the rest. I think sedums might be a good bet, tho I've never had one of the red stemmed varieties do anything other than get straggly; they never turn into a nice clump, but the green/blue green ones do much better at clumping and not flopping. There are so many varieties out there - Gertens or any of the other TC garden centers are bound to have dozens to choose from. Maybe you could find the nice rounded Artemisia "Silver Mound" - that's a plant right at home in a dry location. For a little summer color, I'd make the small investment in a market pack or two of simple old marigolds.

Interesting discussion going on about Astilbes...I have the Arendsii type, planted about 10 years ago under a pear tree. Over the years it has naturalized all over the garden, it has seeded itself in the full sun, shade, semi-shade, even the cracks between my pavers on the patio! I water my entire garden about once a week during drought periods, but this season has been somewhat rainy, so I haven't watered much at all. So, I guess it depends on which type of Astilbe you plant, because I planted a different type in semi-shade a few years ago, and the thing died the first season!! Go figure! LOL. Every garden is different (soils, climate, sunlight, etc.), which makes gardening somewhat of a challenge to see what will survive and thrive. You just have to try things yourself because you just never know! Plants will surprise you all the time...which is what I find so amazing about gardening.

That pink flowering shrub is Coleonema pulchrum 'Sunset Gold', a plant I use quite a bit in combination with succulents in low water use gardens. To keep it this low, I usually shear it with hedge clippers about twice a year, to maintain it extra low. If not clipped regularly, it will get about 3 feet tall by 4 foot across, of course depending on how often it is watered. The street parking strip was converted to 1/4 inch drip soaker lines buried below grade, to avoid run off in such a narrow planter.

That is actually good, since now you have some experience in beheading :) As you can see, the plant survived accident and branched. Looking at existing mix, it may contain some bark - that is good (unless it is all sapwood). You could start making better mix by sifting existing mix (use kitchen sieve) to get rid of very small particles. Buy small bag of perlite, sift it too to get rid of dust, and mix sifted ingredients (larger particulates that stayed inside of sieve) about 50/50. That should give you quite good mix for succulents. (Small gravel, scoria, pumice, turface are all excellent to use for succulent potting media should you decide to grow more of them and put some effort in making your own, well-draining mixes.) Many of my succulents are overwintering in the basement that is dark, and I use lights that are on 14 hrs/day. Give your plant lot of light to grow more compact. If you use light, put it further away from a plant to begin with, moving closer every few days in order to avoid burn (using CFL, fluorescent or LED bulbs helps since they produce less heat, and likely brighter light).