I actually wonder if one reason why they went with remaking a remake (since SF64 is a remake of the original SF on the SNES) is not just because they wanted people who never experienced the N64 version to have an opportunity, but also because they want to reboot it one more time. SFAdv, SFAss, and SFC were decent for SF games, but I didn't like the direction they went with them.
Not saying I agree with their pricing, but for a game about 14 years old, I'm sure a lot of work had to be done to convert a game like this from an old platform such as the N64 to a newer one like the 3DS, since game engines for game consoles at that time were few, far in between, and not very robust. Plus, they went and enhanced it. Of course, if you have the means, you could always play the original on VC, emulation, or even the original on the original hardware just like you could when dealing with any other game that has been ported/remade for these newer generation consoles and handhelds.