I just put Meltonian Leather Conditioner (as recommended by Luccibag on another thread. She has great photos of her bag there.) I am really really happy with how my bag looks. I didn't like it so much on my caviar bags. If I had a new bag under warranty, I would probably take it to Chanel for cleaning. But as my bag is 9 years old and I got it recycled, I had Chanel do a minor repair and I used the leather conditioner myself. It looks amazing.
For the hardware on my bags with gold, I use a gold polishing cloth. You can usually find these at a large department store. I would never use any cream of any kind on gold because it might be abrasive.
Chanel care books do say that gold will tarnish and the gold plating will wear off over time. This is totally true. It depends on how much wear the bag gets. It will usually tarnish first around the holes where the chain goes through. If you use it a lot, the turnlock pin may tarnish. All metal is affected by climate and contact with skin. You can see photos of some of my older vintage belt bags on the post photos of your vintage chanel here. You can see what happens to really old bags that have a lot of use. But some still look like new.
I also think that heat may be a factor in how long the quilting stays soft and fluffy. I have had a few bags where the quilting has compressed and feels a little grainy. I think it is the heat. So I never ever leave my more modern bags in a really hot area. I don't keep them under airconditioning, but I choose the coolest part of my apartment to keep them in.
I also have a hook that I hang behind the driver's seat in my car to hang my bag off while I am driving, that way, it will never hit the ground where it might meet something gruesome left by my kids. At work, I have another hook under my desk for it to hang off. One of my friends has a plastic box under her desk for her bags to sit in.
If you maintain your bag regularly, it should look amazing for years. Some of my vintage bags still look brand new even though they are over 20 years old. Others of my more modern bags are in less good condition, purely by how they were handled.