How much more can I raise my ACT score? (I realize this doesn't have a definite answer)

Your GPA and a 26 ACT are pretty solid for the schools you are interested in, but certainly raising your score will not hurt.

For comparison my son was accepted this past year at CNU, UMW, Gettysburg, and American with a 3.7 GPA and a 29 ACT, 1970 SAT. He is a freshman at CNU and loves it.