Allow 140mph electric trains from Birmingham and London to reach Chester. Allow continental loading gauge trains to reach Chester (this means HS2 captive stock gauges but not necessarily HS speeds on the section). Allow long distance dual voltage trains to reach Hooton (Chester Parkway). And allow the old right of way to be preserved, downgraded or retired and sold off.
The land exists rights there, it is not expensive as land goes, and the topography is close to ideal. Unlike proposed upgrading of the crossings of the River Weaver (either WCML quad-track or Northwich viaduct speed). The low bridge and potential flooding nasties of the old alignment are just the straws that break the camel's back.
Electrifying the Middlewich branch has many advantages, that are unrelated to Chester and Wirral.
There is some merit in electrifying to Chester even if this is the furthest it goes, since most of the London trains terminate there so a lot of running under the wires would be eliminated. London-Holyhead trains would need a bi-mode or locomotive haulage though. I agree with the various people who say that the Welsh Government will need to sort out its priorities before electrification can progress further west.
However in my opinion this doesn't justify a new line. The new line would need as many new bridges as the old line would need upgraded bridges, so the bridge costs would be greater with the new line. With modern clearances and other standards the strip of land for the new line would be much wider than the old one so of much greater area, and the existing land would require a lot of remediation before its value per square metre would approach that of the agricultural land that would need to be purchased. On top of that there is the cost of building new track, drainage and cable routes when the existing ones could mostly be re-used if electrifying the existing line. It would also required legal powers and a public enquiry, at which point no doubt the NIMBYs would start crawling out of the woodwork.
About the only cost saving with a new line would be the ability to build it away from the operational railway. But Crewe-Chester isn't particularly busy, it has no intermediate stations and diversionary routes are available. So it is an ideal route to deal with by a blockade approach which is much cheaper than doing the work during many short possessions.
Even with a brand new line, UIC gauge stock wouldn't be able to access Chester. HS2 as currently planned dives under Crewe in a tunnel and only classic compatible stock would be able to run over the connection into the existing station. Running HS2 captive stock to Chester would need either a new junction at Crewe (possibly underground, with Chester trains unable to call there) or the rebuilding of part of Crewe station to UIC clearances (which would render the platforms involved unusable by normal stock).