The DGX Spark seems to have one intended usecase: local AI model development and testing. The Strix Halo is an amd64 with iGPU, it can be used for any traditional PC workload, and is a reasonable local-ai target device.
For me, the Strix Halo is the first nail in the coffin of discrete GPUs inside laptops for amd64. I think Nvidia knows this, which is why they're partnering with Intel to make an iGPU setup.