MacBook Pro is slow, will adding RAM help?
Upgrading to 8GB will give your more memory-intensive applications a bit more headroom and allow them to avoid unnecessary swap-file usage. Upgrading to an SSD will give a more substantial speed boost overall - apart from dramatically improved OS and application startup times, any applications writing to and reading from a swap-file will also see considerable speed improvements. Your Mac only supports SATA II but the speed improvement will still make the investment worthwhile.