I have installed an SSD into an 8 year old laptop. The speed increase was phenomenal. I use the SSD for multi-booting into various Windows and Linuxes. If you go for a 128GB or 256GB SSD it will not cost that much. Most laptops with upgradeable drives are very simple to upgrade. In my case I had to remove a single screw, pull out the drive bay, pull out the old drive from the drive drawer and replace with the new SSD.
I only have the various OSes installed on multiple paritions on the SSD, and whatever applications I use with each OS. Permanent data is stored on external drives connected via USB3.0 or eSata connections which are also extremely fast.
My old laptop only had USB2.0 ports, but I have an Expresscard port in which I have a USB3/eSata adaptor connected to a USB3.0 hub and an eSata port multiplier hub.