From the results of the vmstat, I would say your server is not even breathing hard much less working so hard it is short of RAM. Looking at the de (which will indicate short term memory deficit) and sr (which will indicate severe memory deficit if it stays high for very long).

The free memory number is misleading. In order to make the most efficient use of RAM, the system will try to continuously use up to the "lots free" setting. When it hits that limit, it will start the page daemon working to free up memory. The system will continue this activity until it hits the "min free" or "des free" parameters at which point it starts wholesale swapping of processes instead of paging. So what happens is that after a reboot you have a large number in the free column, but it slowly will approach the limit that will indicate to you what you have "lots free" set to (you can verify that free matches the system setting with your UNIX Admin -- the numbers should be very close). At that point various memory housekeeping routines attempt to keep that number stable at that point.

This particular information is specific to Sun hardware and Solaris, but most UNIX systems work in a similar method (but the parameters "min free", "lots free", and "des free" may be different). If you are on Sun and want to learn more, Adrian Cockcroft has a good book out (though it is old) called Sun Performance and Tuning, and he has columns in Sun's online magazine covering questions just like this one.

As long as scan rate stays below about 200 or 250 on 30-second intervals you should be just fine.