Boot up time will be MUCH quicker, really.
The pc will run quietly and not get hot.
I could not believe the difference when I replaced my hard drive with a hybrid ssd/hd on my old pc and my other pc has a ssd which is even faster.
You don't need to spend a lot of money to get the full benefits. SSDs are still expensive so a small SSD, say 250GB with the operating system and most used software on will give you speed you want and you can use the current hard drive for your documents and media.