Window Inserts, the Good vs. the Perfect, and Other Big Issues in Small Increments

We live in an old house -- I know, brilliant observation.  

However, when you're a historic preservationist who lives in an old house, you have a lot of concerns about old stuff and yet you want to preserve as much of it as possible.  Also, there's only so much time and money in the day and in your life.  So you find yourself, as I do, thinking about improving things without changing them too much.  Also, there's the planet, and when we can we think about it, too.

Whoever lived here before us used the lack of sight lines to the back of the house to thwart the historic review board and replace everything they could afford to replace.  So we now have about 1/3rd new vinyl windows, 1/3rd old windows with old aluminum storm windows, and 1/3rd just plain old windows.  So, should we replace the remaining windows, or should we just bolster them?

I see a lot of literature about how you should replace your windows for energy efficiency, and the old ones are only single-paned.  However, I'm skeptical.

1. I saw the excellent film Blue Vinyl, and in general I'm aware that it's not a good idea to get cruddy vinyl very close to your home/life/things you value. 
   
2. A lot of energy and effort and resources are embodied in historic building materials. So it's in fact pretty green to keep them, when you can.  
3. I also see a lot of literature about the value of adding insulation to windows and how that compares, performancewise, to simply replacing them. The gist is that while adding isn't as effective as replacing, it's very effective relative to cost and the other factors above. 

All things considered, I've decided to add interior storm windows rather than remove and replace our gorgeous old windows.  (Seriously, look at these.  Gorgeous.)

The three most popular options are Window Inserts, Innerglass, and ClimateSeal products.  These range in price, interaction with professional types, and so on.  But, you know, anything's better than what we have.  Also, I'm not convinced that there's a huge difference between the $80 windows and the $380 windows -- but I am aware that the $380 windows take longer to order and get.  

So, the perfect being the enemy of the good, I'm ordering the inserts.  I will keep you posted as they come in.