atx - here's the deal:

L class fares are pretty much the lowest CO sells. Since free upgrades are prioritized by elite level and fare basis, you're basically at the end of the line for the upgrade. That certainly doesn't mean you're out of luck, but it does mean that you need to hope for flights with low elite loads.

The other stuff you're entitled to as a temporary silver:
-Priority boarding
-Priority luggage handling (ask for a temporary tag at check-in)
-Priority phone line - once elite status is indicated on website, you can navigate to it under the "frequent flyer" menu
-50% bonus miles
-You can also try to change your seat to the "elite" section at the front of coach - probably not worth the trouble.