Arguably, unusual roll cage designs in saloon race cars are interesting, even if it is an aspect of a saloon racing car that probably doesn't make all that much difference to performance (probably with no "correct" solution and alternative designs probably having no real advantage over what one might call a "conventional" design?). It's interesting to see roll cage designs which are different than the norm IMO.
Here's the RML Chevrolet Cruzes from the WTCC with their unique not-door bars running to the top of the main hoop:
This 1995 Vectra super tourer has quite a substantial amount of reinforcement of the engine bay indeed! It seems like it would make installing the engine, albeit done from underneath, quite a pain!
Here's the extra triangulation around the C-pillar of Prodrive-built cars from the 90's and early 00's. The example is the Prodrive-built Super Tourer BMW but Prodrive-built Subaru WRCars used a similar design:
Larry Perkins adopted a somewhat similar double roll hoop design in a push for more rigidity in the early 00's, which was later dropped as being (probably) unnecessary. Note that this Perkins car does not seem to have much bar work and triangulation added to the floorpan however, unlike V8 touring cars built by rival teams around the same time.
The "Larry bar", a diagonal roll bar across the windscreen introduced by Perkins and permitted in Australian touring car racing at the time can also be seen above... It was banned in 2013 on the move of the category to a control chassis design.
Before that though, one team, Garry Rogers Motorsport, even ran a double diagonal (X) across the windscreen which rule makers soon deemed a hinderance to driver vision and banned!
By comparison to the Perkins car, this is the triangulation added to the floorpan of a Stone Brothers Falcon:
Others?