If you take care of a deck, there are only two things that will likely ruin it in the long term - dirt/oil from your hands, and humidity. If your deck ends up dirty or oily, it will be permanently changed for the worse. There are a few things you can do to make it "better", but it will never be the same once it gets gross. Washing your hands is ABSOLUTELY CRITICAL if you have oily skin, if your hands sweat, or if your hands get dirty.
If your deck gets humid, the cards absorb moisture from the air and your hands. Cards are made of paper, and paper + water = bad. Humidity will make cards sticky and soft. This is not what you want at all. The good thing about humidity is that the damage is usually not permanent. Set a deck that is sticky from humidity in a cool, dry place for a while (a few days to a few weeks). If you have a heavy, flat object like a textbook, you can set that on the deck to help prevent warping as the deck drys out. After the deck has dried out, and after you give it a couple shuffles, it will be back to good shape. If it gets soft or sticky again? Repeat the process. If you are in South East Asia, this is a problem you are always going to face. The local humidity will make you go through decks faster than most people.
Neither of these issues really has much to do with the finish of the cards. The finish will be fine if the cards are dirty or humid. The finish is the combination of the textures pressed into the card (the Air Cushion "dimples" for most USPC printed decks) and the actual plastic-based coatings that are applied to the cards. Really friction or liquids are all that is going to damage the finish.
Card clips won't do much to protect the finish or to prevent dirt/oil or humidity from affecting your cards. What a card clip will do is help keep your cards flat when you are carrying them. If you keep your cards in a pocket, a clip is a must to help prevent your deck from warping, especially in a humid area where cards will warp more easily.
I hope this helps!
// L