"HDD has a much higher failure rate than the SSD ..."
While this statement is somewhat accurate as far as it goes, things are relative. While the HDD has a higher failure rate in comparison to the SSD, that failure rate is still very low. A quick peek at two different (somewhat random) drives shows the MeanTimeBetweenFailure of a Toshiba 320 gig HDD at 600,000 hours and an Intel SSD at 1,200,000 hours. Yes, the Toshiba HDD will fail twice as often as the Intel SSD, but just what does that mean to you? 600,000 hours of 24/7 operation is
well beyond the life of the machine. I have been using laptops for about as long as they have existed (my first being a Kaypro 2000 which predated internal laptop HDD's). I do not recall having a single HDD failing before the laptop. To the contrary, I have a number of obsolete HDD's sitting around gathering dust from laptops. Who needs a 2 GB IDE laptop drive? The drive is fine, the machine is long dead.
"Windows 7 does not get along well with HDDs ?" This tech doesn't know what he is talking about, pure and simple. Windows 7 gets along with HDDs just fine. The vast majority of machines running Windows 7 are doing so on traditional HDDs. It was designed, tested and released on traditional HDDs. The operating system doesn't care what type of drive is being used.
The techs at your box stores are not usually the best people to which to listen. A) They have a vested interest in selling you something B) their services are almost always way overpriced and C) if they were the sharpest knives in the drawer, they would be working for someone who paid a bit more.
Again, while the SSD is faster, it only affects - generally - a) boot time, b) application launch and c) battery life. It does not affect your system performance when writing documents, for example. If the original 320 gig HDD is still "setup" with Windows and such, I encourage you reinstall it and take it for a test drive and see just how much difference you experience when doing your work. Hard drive performance, whether traditional or solid state (SSD), does not have an effect on how fast you type, how fast things load/display on the internet, etc.