Is Snow Hill depot anywhere near Snow Hill station? If so, I would suggest that using tram would be better seeing it is faster and can be cheaper (or even free).
Lets close Manchester Victoria at weekends too and save some money, divert everything to Piccadilly.
And, the point was...? My point was that it's convenient for majority of travellers who are looking to connect at Birmingham city centre on weekends and it saves some staff money. Two birds, one stone.
Now I realise it's not feasible anyway.
But you ignore Smethwick Galton Bridge, which as I have pointed out is a popular station and would lose the majority of its services on Sunday with your proposal. You do know it's not the same as the old Smethwick West and that there's no platform on the junction chord, don't you?
The Hawthorns is in a patch of Smethwick where bus services have been reduced by the diversion of the 53 bus. The Metro does not offer an alternative towards the south west. Why would anyone want to go two miles into Birmingham to go all the way out again?
Jewellery Quarter station also serves parts of Hockley and is used even on Sundays for shopping because of visitors to the quarter's many - well, believe it or not - jewellery traders.
As someone who travels through New Street almost every day and even at 2000 and 2100 when you would imagine the station is quieter, still find myself sitting on trains on the approach 'waiting for a platform', I am baffled where you think the capacity for your diversion is to be found.
On Saturday , a quick glance at timetable reveals there are roughly 5-6 tph towards Birmingham and 3-5 tph towards Wolverhampton. Solihull has similar frequencies towards Birmingham and Dorridge.
However, Smethwick has about 0.560 million passengers per year and Solihull has 1.6 million. Nearly 3x annual passenger usage, yet the frequencies are similar. Trains at Smethwick would have no problem handling extra passengers.
Hawthorns and Jewellery Quarter are well served by Metro. Not many passengers from that station are going to west of Birmingham, nor that many passengers coming from West arriving these stations either, at least not enough to justify a dedicated train service when a metro would have sufficed.
Anyway, this suggestion wouldn't work without a flyover/flyunder, capacity improvements at New Street, and possibly Birmingham to Wolverhampton line as well, making this suggestion rather pointless as it was supposed to save on the costs as well making it better for passengers.