Ive been thinking about swapping my MacBook Pro's (late 2012) hard drive for an SSD for a while now, as there becoming more affordable at decent sizes. Apart from the read / write and startup time improvements, do they improve the Spotlight index time of your machine as the image below or is this a process that is carried out by the CPU so a new hard drive wouldn't improve it?
Quite simply, SSDs do everything faster.
Their downside would appear to be a limited read/write cycle lifetime, but so long as you're comprehensively backed-up, I wouldn't see that as an issue.
Adding a Samsung EVO 1TB as the boot drive to my Early 2008 Mac Pro has given it life I didn't know it had left in it.