Whilst the Northern and Western Motorway never came to be constructed, and seemingly had minimal support at the time, it did have an influence on events.
As mentioned, the Government of the day were concerned that the proposal was causing a delay with other planned road improvements of the time, and indeed some did actually suffer a delay - most notably the A580 Liverpool - East Lancashire Road which would have been rendered unnecessary by the proposed stretch of the motorway between Salford and Liverpool.
The Northern and Western Motorway itself had a small revival in 1929, where an altered route was re-proposed, along with a spur to Birkenhead (instead of Liverpool) and a few other motorways.
Perhaps the oddest legacy it left was that when the Ministry of Transport finally decided to investigate motorways more closely in the late 1930s, they initially started work on a potential London - Birmingham motorway - and they started with the Northern and Western Motorway proposals before rejecting the line and slowly moving it to the east until they ended up with the route that we know today as the M1.
However, after then, the Northern and Western Motorway fell into obscurity, never to return...