My thanks to all. Your stories largely mirror my own experience. The Spinners have become dominant and they are fine for airports and modern train stations. As soon as you move onto real pavement and car parks? the wheels get shredded by the tarmac. Getting replacements seems like a fools game as so many places say they can and - when faced with the case - suggest you buy a new one! You can buy replacements online but I'm not sure that is going to work either.
One or two companies are offering removable wheels - at bag drop - so am looking into that. My earliest 2-wheeled cases had retracable wheels and, whilst I saw articles about a new case with that feature - they are all dated 2015 and the company no longer has them on their website.
For journeys to South Africa, we do wrap the bags at LHR but their prices are getting ridiculous. The bag wrap at JNB is cheaper than LHR - even allowing for the rate of exchange! The staff are faster and friendlier too.
I am not planning on going to South America but thanks for the warning.