As bible_pay said, it's probably the other way around - new exchanges should actually increase volume and price, and not distribute volume out and lower average value. At least that's what I've seen in experience with a couple of coins. It's because those new exchanges hold thousands of buyers who are using only that exchange.

For example, take a look at this recent quote from this very thread:


Also, every exchange has some way to discover new coins, so a lot of people first hear about a coin when they see it on their exchange.