It is often the question of rarity that wildly affects the value for these pieces of silver. Below is a table of suggested rarity:
Glasgow (pre-Assay office)
This list is published by antiquesilverspoons.co.uk and is based on the research of Richard Turner (who's book, A Directory of Scottish Provincial Silversmiths and Their Marks, is the authority reference on these towns and their makers).
I have found Aberdeen is by far the most common to turn up (especially the work of William Jamieson!). The towns of Iona and Ballater are both modern producers (late nineteenth/early twentieth century). And the other 'Scarce' towns also turn up somewhat regularly.
Check out my website for examples of silver from some of the towns listed above.