From my experience with this, an SSD is one of the best upgrades you can get. The only thing that will speed up the editor more is a better GPU, or a CPU if you have a really old one, but upgrading from a good to a great CPU will give you less of a speed boost compared to moving from an HDD to an SSD.
Up until recently I used my SSD (250gb) for windows and all programs, and HDD for my projects, but I got a second SSD (500gb) and moved all my programs & Windows over to it using the automatic drive clone tool that comes with Samsung SSD’s, and use the 250gb for my projects. That also increased my load times / shader compile / visual studio compile times, and speeds up the editor even more.
If you haven’t re-installed windows for a long time, that too can give you a performance increase (especially with Windows 7, ver 8.1 seems to manage itself better). So re-installing is actually a good thing, I do it every 6 months to keep things fresh.
Highly recommend an SSD 