Used coffee grounds also attract worms. They also add nitrogen and organic matter and (until they break down) open up the clay a little tiny bit.
I would agree with Cindy: if the clay is soft enough that you can scratch some compost into the top 6-8 inches, do that. It will make those 6-8 inches a l8ittle more open to letting oxygen diffuse down, and will retain more water.
It will also decompose faster than top-dressed mulch would.
Even the beds with plants already established could let you scratch the compost in a little between the plants. But it sure looks nice as it is, and it WILL decompose over time and the mineral nutrients will eventually reach the roots.
>> I'm not sure if I was better off working it in with a fork
When you have your own compost pile going, you can have the best of both approaches: do both. Turn in as much finished or near-finished compost as possible every spring and fall.
AND top-dress with 1-2 inches of compost (finished or near-finished or just started) and/or mulch (coarse) a few times per year after the plants are in.
After you've added enough compost for enough years, top-dressing with compost or mulch will be enough to MAINTAIN soil structure. It helps drainage and aeration that you added sand right at the beginning and mixed it well. Mixing in crushed stone, grit or screened bark 2-4 mm in size will also help create drainage.
But, if you don;t provide and maintain enough compost, the clay will revert to clay or concrete.
