My impression is that the Xerox Alto was a minicomputer, comparable to a PDP-11 minicomputer, and was distinguished by specialized hardware like a mouse, a bitmap display, and ethernet. The Alto fit in a small cabinet. IBM mainframes of that era filled a room. I think that the true analog of an Alto-like computer today would be FoC projects that use specialized hardware to prototype new ways for people to interact with computers. A really good example would be dynamicland.org, which is Alan Kay's current project.

I thought about Dynamicland too as an example of expensive hardware for testing some future of programming!