Having just spent a few stints over in England and seeing a bunch of different courses along the way, the big thing I find striking (and, highly valuable to someone like me looking to see exactly how the old stuff looked, as a means of inspiration for future work elsewhere) is just how much old original stuff remains, even if abandoned.
There are so many remnant bunkers and mounds, even on courses that have done renovations over the years and moved bunkers around. The old ones often have either been left entirely on their own or minimally filled in, the landforms still just sitting there waiting for an edge to be cut and sand to be filled in. A lot of bunkers themselves have only been meddled with on the floors and edges, the key landforms supporting them remaining as is from 100-125 years ago. With more money and care over the years, all these cool, funky, pre-machine shapes would be wiped clean, never to be seen again. That's sad to me for a number of reasons, and it's sad to know some of this is going on and likely increasing in frequency.
A lot of places could certainly be significantly helped out by a little bit of money, but it's only when that money is very carefully spent and allocated to the right kinds of improvements. Otherwise, it's likely just to wipe out history, which is the hallmark of most of these places (and certainly a big element of what makes me want to make the effort to see them).