Author Existence Failure: Subverted. Peter Sallis retired from acting in 2010 due to his failing health, with Ben Whitehead succeeding him for various TV spots, but it was Sallis's eventual death in 2017 that ensured that he'd never voice Wallace again.
The Merch: Shortly after the release of A Close Shave, companies took note of how merchandisable the characters were, particularly Gromit and Shaun. Plush toys, backpacks, key chains, alarm clocks and figurines are just a small helping of products you can find with their likeness slapped on.
The Other Darrin: Ben Whitehead has been increasingly acting as the voice of Wallace, most notably in the Grand Adventures series, along with a number of TV adverts featuring the duo. Fortunately Whitehead's voicing is so near to Peter Sallis that most people don't even notice the difference. The only exception was in "Fright Of The Bumblebee", the first game in the Grand Adventures series. As it was Whitehead's first time voicing Wallace, he sounds a little different than he usually does. Fortunately, he seems to have gotten much better as he continues to voice Wallace.
The Red Stapler: The last of the creameries manufacturing the centuries-old Wensleydale cheese were teetering on the edge of closure in the early '90s, until they received a chance mention in A Grand Day Out. Noticing the increased interest, the creamery persuaded Aardman Animation to endorse a Wallace and Gromit-branded cheese, which worked to rebuild Wensleydale into a thriving product worldwide.
Write Who You Know: Nick Park has stated that Wallace is loosely based on his father, who also liked to tinker, with a little of his brother, an electrician, thrown in for good measure.