Standard disclaimer about paying attention to what MS thinks makes a system good...
Yes the HDD *is* probably holding your boot times back a smidge but it's really up to you. Do you feel you need just a bit more? If so keep an eye on the sales for at least a 120G SSD, you should be able to snag a nice MLC number in the $60 range over the next couple of weeks. Then load everything non-Windows to your current drive.
If not screw'em who cares what MS thinks anyway.
Fair warning. You can't easily restore a Windows 7 backup to a smaller drive. Be prepared for a wipe and reload.
SSD will help with loading times, but will not affect game performance (FPS).
The WEI (Windows Expierence Index) is a total joke. There are computers much faster than mine that get much worse scores, and computers slower than mine that get much better scores. As a general idea for understanding what the next item is that you should upgrade, then yes, the WEI will point out items that are under-performing compared to the rest of the system. But for understanding where you are compared to the rest of the world it is a terrible system.