You would wager wrong, depending on how you define "large." The total exchange volume of all exchanges is only about 93k BTC per day. http://bitcoinwatch.com/
The daily transaction volume, with change transactions removed, averages around 400k BTC per day.
So speculator trade is less than 1/4 of all Bitcoin transactions.
Fun fact: SilkRoad is less than 3% of daily Bitcoin transaction volume
75% of trades are commercial in nature. There are thousands of vendors dealing in BTC- hundreds of which deal in it exclusively. Some are even among the most popular web sites in the world.
25% of the daily volume (100K out of 400K) is pretty huge if you ask me, yes.
How much is money-laundering? How much is people just moving stuff around for the hell of it? Of what's left how much is online gambling (an economic activity but not necessarily a 'good' one)?
These things would be very hard to tell I would have thought.
I would wager that yes, that does account for quite a large volume of the daily exchange volumes.