The only time I think NAS would be beneficial is if I was using System 6 without a hard drive. Start up with a floppy disk on a 20MB RAM disk and switch the boot volumes and use the NAS for everything.

I think it's pretty silly.

What is the maximum throughput supported by the NuBUS interface? That could be your bottleneck. Given that the SE/30 has a peak hard drive transfer rate of about 3MB/sec, I wouldn't hope for much.