I hear this argument quite often and gotta ask... what, you don't have backups? When any of my storage dies I throw the drive away, stick in a new one, and restore from one of my two real-time backups (one on-site, one off-site). For that matter, I don't even trust any HDD that is over 3 years old. It gets replaced whether it reports any errors or not. And I've had plenty of HDDs fail with catastrophic errors over the years. Relying on a HDD to fail nicely is a false assumption.
Another statistic to keep in mind is that SSD failure rates are around 1.5% per year, compared to 5% failure rates for HDDs. And, I suspect, since HDD technology has essentially hit up against a mechanical brick wall w/regards to failure rates (if you still want to pay $80 for one), that SSD failure rates (which are more a function of firmware) will continue to drop while HDD failure rates remain about the same, from here on out. And that's assuming the HDD is powered on for the whole time. Power-down a HDD for a month and its failure rate goes up dramatically once you've powered it back on. HDDs can't even be reliably used for off-line backups, SSDs can. SSDs have a lot of room to get even better. HDDs just don't.
It is also a lot easier to run a SSD safely for many more years than a HDD simply by observing the wear indicator or sector relocation count ramp (actual life depends on the write load), where-as a hard drive's life is related more to power-up time regardless of load. If I only have to replace my SSDs (being conservative) once every 5-7 years vs my HDDs once every 3 years, that cuts many costs out right there. I have yet to have to replace a single SSD, but have replaced several HDDs purchased after that first SSD was bought. Just looking at the front-end cost doesn't really tell the whole story. Replacement cost, lost opportunity cost, time cost (time is money). There are many costs that matter just as much.
In terms of speed, I think you also don't understand the real problem. The problem is not comparing the 100-200 MByte/sec linear access time of a HDD to the 500-550 MByte/sec linear access time of a SSD. The problem is that once the computer has to seek that hard drive, that 100-200 Mbytes/sec drops to 20 MBytes/sec, and drops to 2 MBytes/sec in the worst-case. The SSD, on the other hand, will still maintain ~400-550 MBytes/sec even doing completely random accesses. Lots of things can cause this... de-duplication, for example. Background scans. Background applications (dropbox scans, security scans). Paging memory. Filesystem fragmentation. Game updates (fragmented data files). Whatever.
People notice the difference between SSDs and HDDs because of the above, and it matters even for casual users like, say, my parents, who mostly only mess with photos and videos. They notice it. It's a big deal. It's extremely annoying when a machine reacts slowly. The SSD is worth its weight in gold under those conditions. And machines these days (laptops and desktops certainly) do a lot more work in the background than they used to.
There are still situations where HDDs are useful. I use HDDs on my backup boxes and in situations where I need hundreds of gigabytes of temporary (but linear) storage... mostly throw-away situations where I don't care if a drive dies on me. But on my laptops and workstations it's SSD-only now, and they are a lot happier for it. For that matter, in a year or two most of our servers will likely be SSD-only as well. Only the big crunchers will need HDDs at all.
Nobody who has switched from a HDD to a SSD ever switches back. People will happily take a big storage hit ($150 2TB HDD -> $150 256GB SSD) just to be able to have that SSD. Not a whole lot of people need huge amounts of storage anyway with so much video and audio now being streamed from the cloud. For that matter, even personal storage is starting to get backed up 'on the cloud' and there is no need to have a completely local copy of *everything* (though I personally do still keep a local copy).