I have the Chanel premiere promise eternity diamond band. Bought it in 2017 and I wear that ring pretty much everyday.
Because it's an eternity band, it will not scratch or show scratches that prominently, so I can't say much on scratches but since it's fine jewelry, I assume that the gold will show wear as normally as any other fine jewelry brand. Looking at it now, it looks pretty darn good on the sides of the band as well.
The diamonds are still as beautiful as the day I bought it and they have been set well. No loose or fallen stones.
I only have one piece of fine jewelry and I have not bought any recently so I cannot compare it to the quality of fine jewelry today, but personally, I don't think the quality has decreased over time.
In terms of value, all fine jewelry does depreciate in value since luxury brands hike up the price of fine jewelry A LOT. It's really the brand and design you are paying for.
The camellia is very signature to the Chanel brand and history, so in terms of relevance I can see it having lasting longevity.
The coco crush, while a new collection, the longevity may be there. I remember speaking to the fine jewelry SA about it and he said Chanel had a very very similar collection a while back. As in, they have had this design on their fine jewelry piece before. The design itself pays homage to the famous quilting of the Chanel classic flaps and I personally think it is simple and clean enough to be quite a timeless piece. I have definitely looked at it a few times myself haha. I especially love the ones with no diamonds actually because I love the simplicity of the lines.
Just my thoughts here and there, but hope it helps!