Re: old window Repair vs. Replace debate
In your case I'd recommend improving your existing windows to be a bit more energy efficient. You can apply a low-e film to prevent summer passive heat gains and you can weather strip or overlay with a shrink wrap plastic sheet to prevent winter leakage.
The TOH program has highlighted companies that remove your existing windows and retrofit them with a thermal dual pane glass panel. They also do something to improve the drafty framework of the window, but I can't remember at this point what it is.
I am not a fan of vinyl replacements either, and IMHO, you're not doing yourself or the house any favors to install them. Retrofit widows are ugly, no matter what style or type they are. You can replace the window completely with a "new construction" window that will approximate the look and style of the existing sashes if you're up for that expense. Vinyl in this case is less repulsive, but again, IMHO, not a great improvement.
My major problems with vinyl windows is that they look cheap, they operate with a heavy hand, and in general just aren't appealing. Their claim to fame is that vinyl does not "wick" heat and cold the way that metal windows do, so that vinyl window will sweat just a tad less than aluminum/metal windows. The fact is, when the temps are that extreme, the glass transfers as much or more heat as the frame.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!