You will get faster startup times and read/write times to that drive, is it worth it? yes if you can afford the extra cost.
You can either reinstall everything or use a disk image program like Acrronis True Image to make an image and transfer it to the new drive.
Acronis will allow you to image your old drive to a smaller one, providing that the data it contains is less then the capacity of the new drive.
So it depends on the size of the drive you are getting, if you were to get an 80GB drive the total files on your 500GB drive would need to be no more then about 60GB as you will need some free working space.