Understandable... Well, the bottleneck for a Proxmox Server often is RAM - sometimes CPU cores (to share between VMs). This might not be the case for a NAS-only device.

Another upgrade path is to keep the case, fans, cooling solution and only switch Mainboard, CPU and RAM.

I'm also not a huge fan of non x64 devices, because they still often require jumping through some hoops regarding boot order, external device boot or power loss struggle.