I was looking at a patent mint colored Chanel wallet earlier this year and really wanted it but then was told about the difficulties of restoring/cleaning patent items. One of the examples the SA told me was she had a client who kept her wallet in her bag and it was right next to a receipt- sadly the receipt had stuck to the wallet and all the writing of the receipt got onto the wallet
And there was nothing they could do about it.
The good think about patent is of course- it is "waterproof"- spill a drink on it you wont have to panic as much as you would with lambskin. But from what I've gathered, Chanel's caviar has just the same durability- maybe even more- than patent.
It sounds like you already have a Chanel caviar handbag- so I if you want to get the patent- then sure, go for it. But as someone else mentioned- how about Chanel's lambskin? That is their classic and although it might not be as durable as caviar- its restorable/cleanable compared to patent.