Boot drive (SSD) going read-only randomly
It is possible that you are using a disk driver such as fuse. If so, uninstall it. 

I also have a 2010 MacBookPro with an SSD in my optical bay and a 750 gig drive. I found myself in a similar situation; unable to boot because my data drive randomly became read only at reboot.  

The culprit was fuse. It decided to remove my mount point, and create a symbolic link in its place. 

Try booting into safe mode by holding down the shift key, and removing any fuse like programs. 

Check /Volumes for any symbolic links (Except for the symbolic link to / )

If the issue persists, try creating a new user account. 

Lastly, because both sata ports are sata 2, it is unlikely you would see any performance increase by swapping drive locations.