I own 3 SSD's. 2x 128gb (Corsair) and a 256gb 830. I don't think a single item (upgrade) has provided such a boost to general running of a computer. I won't build another with out an SSD in.
The longevity issues on SSD are a non starter for me. I think most people looking at SSD's upgrade frequently enough to not have any concerns. I am looking at getting a larger SSD just so more software can be run from an SD.