KR is a fine example of a typical RL ground of the twentieth century and an example of the type of stadium we used to see in soccer. It is totally unrealistic but in some ways it is a shame that at least one ground of this type could not be preserved as some sort of historic building.
I think it is the way the old grounds were put together that makes people very nostalgic. They weren't designed by architects etc. A lot of the stands were built when clubs could afford to build them. That makes many of them quirky and unique (e.g. the end stand at the Watersheddings and Willows, Snookers club side at Wilderspool, the changing rooms at the corner of Thrum Hall)
Many fans would pick their spot and happy reside there for many different reasons. I must admit though that I would prefer new stadia to be built on old (e.g. Widnes) than they flattening and moving to a new site - but economics and geographics determine that. The biggest shame was the Wigan saga where, at the time, Whelan wanted to re-develop the old Central Park. How awesome would that have been? I understand that problems at the time prevented this.
I agree with your post. Yes, stadiums were a collection of buildings erected as and when clubs could afford them - and need them! You could usually tell which rugby and soccer teams had had periods of success, and the consequent crowds, by the size of the structures contained within the grounds. Perhaps that contributed to the 'soul' of the place - that substantial grandstand reminded your grandfather of the massive popularity of the game in the 40s and the club's success then (as he never used to stop telling you!)
Also, because the ground was usually developed piecemeal, and they were usually developed in highly built-up areas, the individual structures had to fit in with what space was available. So, when Oldham had just a narrow strip of land behind one end of the pitch, but still had substantial crowds to fit in, what do they do? Build a double decker. When Saints build a grandstand but the railway encroaches on the space - erect a structure that ends two thirds of the way down the pitch.
These quirks made the place unique and helped it to feel like 'home'. What matters today, however, is comfort, safety, decent facilities and a good, unobstructed view of the pitch, and is quite often better financially to construct this on a new site where the pitch is plonked in the centre with the stadium built symmetrically around it. No need to adapt the buildings to the differing layouts of the 4 sides and so a standard design can be used.
I agree that rebuilt grounds do tend to preserve their character better and, I think, Spotland is a fine example of this. The redevelopment started with the grandstand, a modest structure because the clubs only had a limited amount of money available and needed to incorporate all the offices, changing/training rooms, restaurants, hospitally boxes etc. (Also it had to be built around the existing pub built in the stadium grounds.) Next came the 'home end' for the soccer club, a larger stand where the home fans could congregate behind the goal, drink in the pub down below, and try and create some atmosphere. The last rebuilding was the northern side of the ground - here came the realisation that, given the limitations of the 'main' stand, this would need to be a more substantial structure to get the capacity up to the 10,000 needed should the clubs achieve success or attract representative games.
Lastly, the most modest part of the ground, the small covered terracing behind one goal, was re-clad, repaired, but left more-or-less untouched - its early sixties design acting as the architectural inspiration behind. So, a piecemeal development, built as the resources became available, but in an already well-defined site layout, became what is now, IMO, an attractive and interesting 'home'.
Add the substantial crowds
and it will have 'atmosphere' and 'soul'