Bamboo or other prolific tree in between the crevices and trust they will find the dirt they need? Or you could rebuild the lower wall 2 feet in front of the existing removing the existing/reusing little by little as you go. Add more dirt. This increases the planting space. Put some tall trees that.match the trees behind the wall in your neighbors property (different kinds of palms, bamboos, tropical plants plus beaiganvilea), depending on light conditions.

Wow - the fill they used in that lower tier IS ugly. What about topping it all with a nice flagstone to make your seating area, and then planting the top tier with smaller greenery to bring some softness and color to the are?

Adding seating would be a waste of money as no one will ever sit on it with the hedge there.

Yeah, I don't know that they need seating, per se. But what is there is undeniably ugly and so topping it off with something will improve it regardless.

A cheaper option would be to top it off with better looking stones - river rock, maybe?

It looks like dirt in the lower section. The ugliness is the upper section next to the fence. How tall is that from the ground? If it is high, it could be filled with gravel.

Here are a few ideas:

Can you paint the fence a warm brown? The black is kind of harsh.

@simplynatural thank you, that was essentially what i had in mind. Im based in queensland, Australia. the area gets hot sun all day.

the wall is roughly 12meters wide. i was thinking building a timber seat in the middle (roughly 5m wide) then creating a garden bed on either side and filling in with a nicer mulch.

i would remove the hedge below in front of the seat.

for the top i have a climber which actually seems to be growing fine in the small amount of soil. ideally i want this to grow along the timber wall.

i like your idea of cascading gardens but do you think planting these in small plater box would work well considering the cement up top? Ideally going for a more formal garden look. i like pops of colour against the dark colours.

thank you all for the suggestions :)

Had to think about this for a while. I have never lived in a warm climate (much less Queensland), so I don't know your plants. You also said you like a formal garden look. To me, with just pictures and a trip or two to Florida to go by, "formal" and "tropical" are opposites. Formal is quiet; tropical is flamboyant. Formal is controlled, tropical is wild. Formal is geometrically ordered, tropical is plants with definite minds of their own, growing every way, everywhere. So how does one make a formal tropical garden?

Here's an attempt. I matured the hedge, made a seat on part of the lower wall, as you proposed, with an extra raised planter for a back to support pillows. I "grew" your small climber (bougainvillea?), pruning it into a living artwork on the dark fence. The climber is bright red, so I eliminated the bright purple aubrieta, kept the Silver Falls dichondra. (I would at least try one small start of it at the base of the fence, giving it as much soil as you can, and see how it does. If it can't find enough resources to survive, you haven't lost much, and if it does well, you could then get more.) I added other touches of red, silver/green, and blue/gray, deliberately choosing some plants (sedum Sunsparkler Dazzleberry, near the patio and behind the bench) that repeat the fence color to integrate it into the garden. I noticed a very young tree in your photo, so I "grew" that, too, and planted around it (star jasmine, counting on some shading for it eventually from the tree), but I don't know what it is so didn't add leaves (and the growth pattern shown may be all wrong). Other plants left to right are Westringia fruticosa 'Grey Box', Alcanterea 'Silver Plum', a kangaroo paw, a grevillea beside the bench. Choices made mostly visually, with very little research; please forgive my ignorance of appropriate plants for Queensland and make your own choices! But maybe some visual ideas to consider.

And just to satisfy my curiosity, what is the object on the left that looks like an enormous plant pot?

I would be tempted to add more potted plants, like the one on the left, except rectangular pots to fit in your area