As far as developers are concerned, the integration of Grand Central, OpenCL and a 64 bit kernel will allow you to take full advantage of the dual processing power of Intel Macs. If your Mac is operating at a slow pace, then for that reason alone it is worth the upgrade to OS X 10.6 Snow Leopard.
This version of Apple's OS also has a reduced footprint. This update does not have stacks of new features, rather overall improvements and efficiency upgrades. You can purchase Lion by contacting Customer Service: Contacting Apple for support and service - this includes international calling numbers.
Mac OS X 10.6.8 Snow Leopard is an upgrade to the previous version of OS X Leopard. After you install Snow Leopard you will have to download and install the Mac OS X 10.6.8 Update Combo v1.1 to update Snow Leopard to 10.6.8 and give you access to the App Store.