Here are a couple of other ways to get the area of something like a wing tip. These methods will get you probably within +/- 1 sq in or so. Some may have already been mentioned.
Make a full size outline of the wing tip shape. Depending on the shape, a triangle can be drawn inside that shape, like the base would be at the chord line where the curved tip shape starts and the legs of the triangle would go to the very end of the tip. Measure that triangle and calculate its area (1/2 the base times its height). Then you can draw two more triangles one at the LE and the other at the TE, using the two lines from your first triangle as their bases. These will probably be very slender triangles (long base and relatively short height). Calculate the areas. Then depending on how much accuracy you want, continue to draw successively smaller triangles until you have the entire tip described by triangles which will give you a fairly accurate area of that tip.
Another way and you have touched on this is to draw the full size shape of the tip on a paper that has a ruled grid showing 1" squares which is further subdivided into 1/4" or 1/8" or even 1/10" squares. (You can get these sheets in pads from drafting or art stores.) Then count the full one inch squares, and then go on and count the remaining smaller squares. Keep track of the smaller squares that are divided by tip outline to be only a fraction of a full square and add the ones that are say 1/2 inside the tip outline, or 1/3 inside the tip outline, and so on. You can get a total area measurement that will be within a fraction of a square inch of being accurate.
Either process does not take much time.
A planimeter works great if you have access to one.
Keith