Jeanneau 37, Great Lakes to the Caribbean?
Probably not as much as you think.
I''ll make a translation of the photo subtitles, beginning by the solar panels and turning clockwise.
1- Directional solar Panels.
2- Better isolation for the refrigerator. Refrigerator with an eutectique plaque (water refrigerated).
3- Device to prevent a crash boom.
4- Spinnaker pole mounted on the mast (preferably carbon).
5- The connection between the mast and the boom should be strengthened.
6- Zenithal hatches with sun covers.
7- A better genoa (Radial and stronger).
8- More space to store cloths.
9- Inox protection of the bow.
10- Removable jib stay.
11- Better ventilation of closed spaces like the head with solar ventilators.
12- Better ventilation - Dorades.
13- Traditional system that permits you to transform the settee in a true sea berth.
14- Watermaker under the settee.
15- Installation of a battery monitor.
16- More batteries.
17- Bigger alternator.
18- Transformation of one of the cabins in a food storage space.
19- Performance propeller (retaining the fixed one as spare).
20- Liferaft in the transom.
21- Wind Generator.
Probably the costlier modification is the one in the refrigerator system ($5000).
It is very important because energy is one of the main problems (aggravated because the boat can not carry big tanks) and the refrigerator is, by far, the biggest energy consumer. With the proposed alterations you need less than 50% of power.
About costs, in that article they give some examples with prices of standard boats (new) and the price needed to equip the boat to the article specs. One of the Standard boat costs 144 300 euros (Bavaria 42), the "Grand croisiére" boat (Bavaria 42) costs 216 406 euros, that is more 50%.
The decision to sell versus modifications will (in my opinion) depend of the optional equipment that you have already in your boat