I'm not sure I really understand where you are coming from with this. If you think the S30 "shone" in the US racing scene, I'd come back with the counter argument that it was - essentially - superannuated club racing. Essentially private teams supported by sponsorship, no great level of factory support and rather 'local' rule sets and class structures. Some of the teams running 'Datsun' branded product got money and a few parts from Nissan USA, but it was not a factory effort was it? I often see our American friends happily stating that Datsun 'beat' Porsche in SCCA racing. Meanwhile Porsche was wrapping up the Sports Car World Championship of Makes in 1970 and 1971 and the International Cup for GT Cars in 1970, 1971, 1972 & 1973.
I've said it many times but I'll say it again. Nissan's single most important market has always been its home market in Japan, and that's where you can expect its priorities have always been. Racing and rallying activities have had to be framed in the context of brand and product promotion. The 'Oil Shock' of 1973 had a huge effect and Nissan - along with the other Japanese manufacturers - had to rethink their plans and try not to fall foul of popular opinion (where racing and rallying suddenly became seen as frivolous and wasteful) and it had a lasting effect. It should be no surprise that this had an effect on their international racing and rallying plans or that most of the satellite operations outside Japan were left to look after their own local sporting ambitions.
The situation for Nissan today is just as difficult. We are fast approaching a state of mind in the majority of people that sporting cars are somehow decadent, gauche, selfish and bad for the planet. Here in London there is a very militant minority taking control of local government and they are determined to restrict and ultimately ban private car use and - by extension - ownership. We know where this is going. A manufacturer like Nissan (they are not Porsche...) has to be seen to be promoting products like the LEAF. For some years now they haven't really been able to tell us what the successor to the Z34 will look like or how it will be powered, but I don't blame them. They are between a rock and a hard place there.
I certainly don't understand the comment about the Skyline. There was a time where the Skyline brand was one of Nissan's flagships, but now it has been divested of its premium model (the GT-R) it seems almost doomed to middle-aged bloat. It always was a Japanese domestic phenomenon - its export sales effort being minimal - but it is being crowded off the road by hateful mini vans and faux hybrid boxes which have more in common with white goods. NO FUTURE.