Ok, lets look at some numbers. For one pound of lead you can cast 110 .36 cal roundballs, or 150 .32 cal roundballs. 40 shot advantage to the .32 (miniscule) 1,200 fps with a .32 can be reached with a mere 10 grains of 3F (1,200 fps chosen as a reference point due to the common velocity of .22 long rifle ammo being aprox that speed) while the .36 requires 15 grains of 3F to reach the same velocity. A one pound container of 3F holds 7,000 grains of powder. The .32 will give 700 shots per pound of powder (at the 10 grain 1,200 fps level) while the .36 equalling the velocity with ease requires 15 grains per shot returns 466 shots per pound of powder. Again advantage to the .32 233 shots per pound of powder.
Costs per shot advantage?? At aprox $15 for a pound of Goex (plus shipping and haz mat fees and idiot tax etc) each grain of powder used costs $0.002 So if you get your lead for free it costs you 2 cents plus the price of a cap or a flint and powder to fire your .32 at the above level. The .36 costs 3.2 cents in powder to fire at the same velocity. Put another way over the life of the gun if it is fired 5,000 times the .32 will use 7.1 pounds of powder, and at the $15/pound cost $106.50. The .36 will use 10.7 pounds at a cost of $160.70. Advantage .32 by $54.21 yes it is a slight advantage, but there is a real difference in the cost of operating a .32 vs. a .36. The power difference is just as miniscule, but there is a difference.
Load each with 30 grains of 3F and you get a suprise! The .32 launches at 2,100 fps and returns a muzzle energy of 462 f-p. While the .36 loaded with the same 30 grains of 3F only reaches 1,764 fps with a muzzle energy of 449 f-p. Advantage to the .32 by over 300 fps and 13 f-p muzzle energy.
I question the versatile argument when only shooting patched roundballs.