You want transaction volume, not total value outstanding, to help a market absorb larger transactions. The impact of a particular trade on a market is determined by the amount of trading going on (in particular, the size of the unfilled bids and the depth of the bids -- how much is available to trade, and how far away from the current market price is each potential trade.) At its most simple this is represented by the bid/ask spread, the gap between where you can buy and sell at a given moment - in more liquid markets, this gap is smaller.

Generally, a market where there are lots of transactions going on is going to have a bigger set of bids and asks right near the most recent transaction price. If a market is thin, than a large sale, for example, might have to chew through a lot of bids and push the price way down to get done.