Well spoken Oberon. Sometimes it doesn't even occur to people in the industry that restoring windows is a viable option.
RESTORE YOUR WINDOWS IF:
1. You want to as much as possible preserve the historical authenticity and charm of the home.
2. You don't mind the hassle of washing windows from the outside, and washing storms windows. (Decide if you want to keep the old storms, or replace them with wood, alunimum or vinyl storms)
3. You don't have excessive condensation issues and the comfort level in the home seems fine with the existing single glazing with storms.
4. The windows are not badly rotted.
By restoring the windows you can make them (somewhat) more airtight, work easier, spiffy & clean, and BEAUTIFUL.
REPLACE YOUR WINDOWS IF:
1. You want them to be significantly more energy efficient.
2. Low maintenance (you could get a clad exterior with a wood interior).
3. Have windows that tilt in for cleaning.
4. Possibly eliminate the exterior storm window and have a screen only (but this somewhat changes the look).
5. Have better sound blockage, potentially easier to operate windows, and greatly reduced fading from the sun through the glass.
6. If you can afford it and are willing to do so.
If you replace them, I'd recommend not removable grilles, not metal grilles between the glass, but instead get permanent non-removable simulated divided lites. The muntin bars are always clean and sharp-looking, never need painting on the exterior, and can be made in the identical pattern that you currently have on your home. They would be pretty costly though. Removable grilles generally cost about $4 per pane, and permanent non-removable lites about $15-$25 per lite depending on the brand. For non-rectangle shaped lites like yours, it's maybe an extra $15-$25 per rectangle lite plus $40-$50 per curved lite, PLUS the cost of the window and installation. So it can add up. Attached is a simple picture of a new replacement window with simulated divided lites instead of removable grilles.