Those numbers are not worth valuing that much. It was meant to help more easily tell the performance difference between machines, such as when looking to buy a laptop and you needed an easy way to compare performance. I believe Windows 7 was the last version that included Windows Experience Index numbers from control panels's system view.
I also wouldn't say the 6.9 rating is "out of line". Unfortunately these subscores don't give a real measurable way to tell what's going on. In the case of a storage disk, read and write rates (in MB/sec, for example) give something worth measuring and comparing.
In other words, I wouldn't be worried about Windows Experience Index numbers.
Trim is not something that runs all the time. Windows (or whatever operating system you're running, as long as it supports TRIM commands) will tell the SSD when to Trim the drive. If memory serves, Windows 7 and later enable this automatically for SSD drives, and there's nothing more for you to do.
Regards,
Aaron
