According to the recent Google SSD study (involving SSD's they use in their data centers), age plays a bigger role in SSD failure than usage. So, according to the study, rotating usage won't add to the SSD's lives. Besides, with current SSD's, technological obsolescence will probably happen before SSD failure. But backup is still important as SSD's can fail. I think the study said backup is even more important for SSD's vs. HDD's but I may be thinking of another study. You can search for "Google SSD study" if you want more information.
I use a RAID0 setup (what duervo described in post #2) in my 2012 MBP. I think that unless you have specific applications that can take advantage of RAID0, there's not going to be a noticeable performance improvement. (The Blackmagic benchmark numbers are impressive, but if look on the web, it'll backup my assessment.) I use EyeTV for DVR recording and when I need to edit a large number of shows (mega-marathons), because there's a lot of file reading/writing of large files with little processing, the performance gains were substantial (I tested it RAID0 vs non-RAID0 with the same SSD's). So I'll continue to use the 2012 MBP for this. On the other hand, I do monthly processing using a MySQL database and in some of the operations, my 2012 MBP with 2 Samsung 850 Evo's using RAID0 was faster, in others, my 2012 Mini with a single, older OCZ SSD was faster. In the end, the trouble of moving the data from one computer to the other was more work than any overall performance gains so I still use the 2012 Mini for the monthly processing. There maybe database tuning that would make RAID0 faster, but unless you have such an application and the expertise/time to do tuning, it's not a factor for most people.
Getting an SSD twice the size is slightly cheaper than two drives (depends on the price du jour).