I think half of the problem is - especially the earlier ones - is that theyre rot boxes with steel body frames and were often beyond economical repair. They're also well known for their electrical faults and a right pain to keep going.
I own an 07 plate VDL SB120/Wright Cadet, I've not had it long, but I don't really have any interest in taking it to running days. Very rare I go to running days at all, but when I do I'm more inclined to ride 80s/90s era buses. I do love a ride on a Bristol RE though!
It seems pointless me taking an 07 plate Cadet which is still in Arrivas current livery especially when another of the batch is still in service in Bangor. Yes it has some enthusiast appeal for the younger lot, but would do absolutely nothing for the majority. I bought it to prevent it being scrapped because I quite liked driving them, and it was a case of if I don't buy one nobody else will! Maybe when i've "restored" it, time will tell.