Most of my Blyton books as a girl were my mum's copies that she let me have, and modern copies (80s) that she bought for me.
The Adventure series were all my mum's apart from River (which she bought for me) but my FF and SS were all bought new.
Sea of Adventure was the only one I had with red cloth boards and paper cover, although I don't know what edition it is without looking, and I've not got it here with me. That must have been my mum's when she was a girl, funnily enough I've never thought to ask her if she had others! I've never seen her with any other old editions and there were never any about in our house (apart from Sea) when I was a girl, so if she did have any they must have either been lost or given away or something. Maybe she left them behind at her old house when she and my dad bought their first house; Sea is her favourite so maybe she just took that one with her!
The rest of the Adventure series I had were the 1975 Piccolo editions, which my mum must have obviously bought for herself when she was a young woman in the 70s. She was born in 1951 so she'd have been at least 24 or 25 when she bought them.
Even though those Piccolo editions had slightly more modern cover illustrations, they're the ones I am very fond of because I grew up reading them and that was partly how I imagined the children to look. I say 'partly' because obviously I also had Sea with the original Tresilian illustrations, and the Piccolo ones also had Tresilian illustrations, so I was imagining them as both Tresilian and Piccolo!
I love the traditional Tresilian illustrations, with Lucy-Ann and Dinah looking like well dressed girls of that time, with their curly hair styles etc, but I also love the 1975 covers too, with Lucy-Ann with her straight red hair.
However, even though the Piccolos look modern compared to Tresilian's, they're still not obviously ultra modern, and the children are wearing simple shorts, jerseys and rubber shoes etc, so they still look pretty traditional to me; its not as if they'd been updated to wearing flares etc!
My FF books were mostly the 1987 Knight ones (where they look like members of Duran Duran on the covers!) and the 1992 Award ones with Jolyne Knox illustrations. Again, nowhere near the originals and I definitely prefer the Soper illustrations, but the Maxey and Knox books retain a charm and I have real fondness for them because I grew up with them.
Sorry for the long post Nigel, hope you'll forgive me!