I would consider SSD's still very important even with Sata2. In fact, I would even consider SSD's still relevant even with SATA1.
One of the largest performance increases that SSD's provide over mechanical drives is random 4k reads and writes and average latency to read/write data.
Typical 4k read speeds for SSD's are roughly 100MB/s still below SATA1 speeds. Typical 4k read speeds for HDD's when data is not cached is roughly 1MB/s.
For sequential loads, however, I will agree with you.
I agree with you, even using ATA33 SSD is a improvement over HD, but, why limit your potential performance with the older interface, if you can buy sub $50 sata III boards for the Intel solution?