Will that improve the speed of my site and if yes will that really be noticeable?
I have about 10 concurrent users at a time on my site...site is mysql involved and does a bit more I/O then average site.
My average usage of memory is only 400MB, never seen jump higher then 500MB.
A full dedicated server would certainly be more power than a VPS, but it may not result in a noticeable speed increase if you've only got 10 concurrent users. Does your site seem slow now? If so, there may be other things you can do with your current setup to tune things, either at the web server or MySQL level.
Well it will have more RAM and the hard drive usage is all yours, so it should be faster than your current VPS, but you will be losing your raid protection, unless you chose to have raid 1 with 2 drives when ordering, which could cost more.
Really depends on your website, could you provide a URL so I could take a look? Server speed is really dependent on CPU/RAM more than anything else. Unless you are using IDE drives which I doubt you are... since that is no longer the industry standard.