SSD for new Mini Server?

Hi, guys!
First time poster here

I would like to know your opinion on the following:
I am planning to go for a new Mini Server and run it in pair with an external Thunderbolt RAID storage. All shared data will be stored on the external RAID, while the internal Mini's disk will be used for running OS, storing account data and running basic services like File Sharing, Print Sharing and VPN. The question is: will I benefit from replacing the default 7200 HDDs with an SSD?

Of course, the machine will start faster and generally run smoother, but I don't really care about that as I will hardly ever see its interface after the setup is done. I am interested in whether SSD will contribute to increasing speed when my users will access their data (stored on the external RAID)? The access chain is as follows: Client computer - LAN - Mini Server (with HDD or SSD) - Thunderbolt connection - RAID.

Another question that bothers me is redundancy, of course. With 2 HDDs I would make a RAID 1 massive to provide for user account data redundancy. To achieve the same goal with SSD I would need to add a second one, which is getting quite exepensive, frankly speaking But this is a completely different issue, I guess.

Would greatly appreciate any feedback.