is the 1990s "WIDE MODE" setting the 'soundstage' of today, and a gimmick?

There were a couple of versions of this. Some used comb filters, others simply blended in the anti-signal from the other side, and some reversed polarity completely. 

 

When i read reviews of someone swapping in a new device, and is experiencing a new breathtaking soundstage,

I literally had a thread devoted to the topic of reviewers claiming that the new device is so revolutionary they have to listen to their entire music collection all over again, and IMHO it's bullocks.  Just the reviewer trying to justify their existence.

I had an EQ that had an "Expander" button, or some such thing on it.

Sounded awful then, and I'm sure it still sounds awful.

:)

Implementing a processed signal to imitate a big sound field as you point out is not new. It has been done on low FI stuff for a long time. Actually the iPad does an amazing job of creating a big sound stage.

‘But a new high fidelity piece of equipment has to do it by great fidelity. Fooling sound with the signal always creates fundamental sonic problems.

One piece of effective tech that created nearly a 360 degree sound field is Q Sound. But this is processing done in the recording. Roger Waters, Banco de Gaja and a few others have used it. In Amused To Death you can hear a dog bark behind you… among other amazing tricks. This technology allows you to keep fidelity. In some of the Banco da Gaia… Maya (I think)… the strongly low frequency music moves out from the the sound stage all the way to one’s side. Amazing really.

You can google Q Sound Recordings to get a list of albums using it.

IFI 3D Holographic. 

I a BBE 25 years ago but it wore out.

Electronic gimmickry like that is fine on less expensive gear, like a a boom box. But it is a detriment on higher end gear.