I loved playing the EV series. You got the series a bit mixed up, however. Override came before Nova, and Override is a Mac Classic only application, just like EV Classic.
One way to get more game for your money is the use of plug-ins. I actually never installed EV Classic, but I played it using the Override engine by downloading the EV Classic plug-in. There are plenty of story line extensions and even story line replacements you can play using plug-ins. What's even more fun is the extra ships and equipment you can get from plugs, my favorite was the starship Enterprise-D. If you want to get into hacking it, make sure to get ResEdit for Mac Classic, which will let you modify all kinds of parameters for both plug-ins and some built-in features.
The website shows that Nova has plug-ins to give you both the EV Classic and Override story lines. I only played it on my brother's Windows machine, though, so I never tried the plugs. I really liked Nova, it had a very rich story line with a lot more paths to take than the first two installments.
Escape Velocity: Classic Mac Gaming at its Best