While there are definatly some mods that apply strictly to specific vehicles, most mods are universal.
For instance, the Escort ZX2 likes more ignition timing and a cheap way to do this is a 5.6ohm resistor on the IAT sensor wire. You get a couple degrees more advance and a little better mpg. Things like this do not work on all cars. Grill blocks tend to work on everything though. I'd focus on the Universal type mods and study Elantras to try and figure out what issues they have that can be corrected to improve mpg/performance...although performance mods don't pay for themselves.
You've already got a great start. You just need to apply your mods carefully to your "commute". IE...aeromods don't help in stop and go traffic...etc...
The only thing that will limit your ability to go far beyond 40mpg will be your wifes willingness to sacrifice looks
but she did marry you, so maybe she won't mind some plastic hanging off the sides
Just Kidding LOL!