What are some central ways in which DSP plug-ins are made to sound different, even if the basic algorithm is common?

[soundmodel]

There is plenty of neglected design space for complicated and/or computationally intensive processing.

Yes, so like U-he Diva?

U-he Diva seems very well designed, but it is complex because it consolidates and accumulates many traditional features of vintage hardware and allows to use them together, not because of obvious novel designs. An assortment of filters and oscillators that sound good is certainly a more creative design than pedantically emulating specific hardware, but it is still a modest step forward.

No the reason I gave Diva is that I think I read that it's an advanced circuit model. I cannot find the article now, but it said that Diva was related to attempts to produce the equivalent of a SPICE model of analog synths, but which is too compute-intensive to be ran in real-time.

Based on some threads Softube has a similar approach.

So based on "plenty of neglected design space". Well, surely one could want to scale those up, but I assumed it's not possible without new computers.

[BertKoor]

it's an advanced circuit model

A what ?

Page 2 is interesting, but you've read it all before. There's no really new information to be gathered here.