Don't be concerned about the lifespan of an SSD device on a stand-alone computer like your laptop. If you do the math, the expected lifetime write capacity of your SSD runs to tens or hundreds of petabytes. That's a lot of stock quotes. The keyboard, hinges and display backlights on your machine will fail from wear long before the SSD will. I have an X-25 drive that serves as system drive (drive c:) on my HTPC machine. It runs 7/24 and has done so for more than 18 months. Intel's SSD toolbox software reports remaining life is still 100%.
If you're really worried about it, however, even though Silverlight installs to your system drive it's not very write intensive on it's own (mostly a collection of libraries that are read by other applications). The application (the stock charting program in this case) may let you assign data collection/storage to a separate storage device.
The other way to look at it is even if the SSD proves to have a service life that lasts only as long as the 3 year warranty period of the device, the replacement will be twice as fast, hold four times as much data and cost half as much.
Enjoy your drive, and may you have better success at day-trading than I have.
