I've seen the isolated damage too but I don't think it has much to do with silica in the case of tomato since tomato plants don't utilize much silica. Nonetheless I think adding a silica source that will convert to silicic acids is a good idea since silica is lacking in most container mixes and fertilizers. Most natural soils are abundant in silica and silicic acids. Silica is not an essential nutrient but it can't hurt to have it available. It's much more beneficial to plants that utilize much more of it like cucumber.
Calcium is much more important to tomato plants in part because of its role in building up pectin that strengthens the cell walls.
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