New Undergroud Station in Church Street?

[Waterways]

But central London is huge & actually warrants so many stations & them being close together. Liverpool city centre is tiny in comparison, so I really don't see the need myself.

You have missed it. In areas of high passenger congestion it is needed irrespective of overall city size. In the City of London on the same road they are only a few hundred yards apart.

Church St, Liverpool One and around is an area much like parts of London in traffic use.

In Paris the stations are so close, you can see other stations looking down the tunnel. I once counted 4 stations. They use the Metro like bus stops.

Although I would like to see a new station round the St James area, serving Upper Parliment St / Park Road & perhaps another in between Moorfields & Sandhills, serving Vauxhall & the waterloo Dock complex.

St. James' is waiting and there, and earmarked for opening one day. When the area becomes more built up then it will open.

Also, Waterloo Dock, at the end of the Waterloo Tunnel and Northern Line is a prime candidate.