Not unless you're sometimes running some software(games for instance) from the storage drive, or often load a large numbers of documents/pictures off it.
Nope. That pretty much means that you agree with me that it would be useless.
To me this whole separate SSD-caching thing ought to fast become a fad as SSD's keep dropping in price, though I can certainly see a use for it in laptop models where the customer wants to have a large integrated storage space.
Perhaps it will be useful for a few people, but as you say not for the vast majority.
If you have spare memory slots and often keep the system on constantly over a day, adding more RAM might be a worthwhile boost for general drive cache. RAM is so cheap today if all you'd need would be two 4GB sticks. I toy around a bit with RAM-disks and toy with the idea of going from 16 to 32 GB.
For some people that might be worthwhile, but not for me, I already have 8GB of RAM and an SSD, and rarely keep my PC on overnight so even more RAM would be worthless to me at the moment.
One of the reasons why I asked the question is whether a Hybrid drive would be any better under the circumstances I have outlined - it would add no performance benefit from the SSD component and would cost more for the amount of storage it provides - its only benefit would be that it would spin down the drive more frequently - but that might be a bad thing from my usage as it would also spin up more regularly as well.