EVPN multi-site for multi-tenant single-DC design, and connection of non-VxLAN leafs

I'm evaluating an EVPN multi-site design for DCI, to connect a legacy and new DC so I can migrate workloads without readdressing, whilst minimising shared fate between the DCs. There's a mix of large STP domains and L3 leaf/spine designs in the legacy DC, with a common core switching layer connecting them to the WAN.

I'm considering consolidating that into an EVPN multi-site topology in the new DC (e.g EVPN multi-site for multi-tenancy inside the new DC not just for DCI, mapping availability zones in the DC to site-internal fabrics for failure domain separation).

I'm keen to know if others have had success operating EVPN multi-site as a multi-tenant single DC design, or is the additional complexity not worthwhile?

Is it a valid design to use a single set of spines to connect the VTEPs and standard L3 ToR switches, or do you use separate spines for the EVPN and non-EVPN parts of the network?