My fiance and I also own an older home that we are remodeling. It is over 100 years old and has plaster and lathe walls with no insulation. As we are removing the old walls, we are insulating and putting up drywall. By all means, while you have the walls exposed, insulate. You just cannot go wrong.
If you are doing this yourself, make sure you are using the right grade of insulation or you could be wasting your money. Example: 2x4 joists usually use R-13 or R-15, not R-19. R-19 is usually for walls that have 2x6 joists. This is important since if you use thicker insulation for your wall joists size, and are therefore crushing the insulation a bit, it decreases its value. This information is per: insulation contractors. I sure hope this helps. Good luck with your projects.