Showell's Dictionary gives an interesting description of the Crescent and Wharf. It sounds less upmarket than I thought. looks like the land was leased from the Grammar School:
"When built it was thought that the inhabitants of the handsome edifices here erected would always have an extensive view over gardens and green fields, and certainly if chimney pots and slated roofs constitute a country landscape the present denizens cannot complain. The ground belongs to the Grammar School, the governors of which leased it in 1789 to Mr. Charles Norton, for a term of 120 years, at a ground rent of £155 10s. per year, the lessee to build 34 houses and spend £12,000 thereon; the yearly value now is about £1,800.
On the Crescent Wharf is situated the extensive stores of Messrs. Walter Showell & Sons, from whence the daily deliveries of Crosswells Ales are issued to their many Birmingham patrons. Here may be seen, stacked tier upon tier, in long cool vistas, close upon 6,000 casks of varying sizes containing these celebrated ales, beers, and stouts. This stock is kept up by daily supplies from the brewery at Langley Green, many boats being employed in the traffic."
So as well as the change in european markets, maybe they didn't anticipate the full impact of the popularity of the canals. Viv.