Water meter still spinning even after shutting off water to house

As a guess, the pipes got layered internally in scale, that will come out over some time (dissolving into the now softer water). Some large chunks may require filter screens, shower heads and valves to be soaked in your vinegar or CLR (containing lactic and gluconic acids).

I know boilers get descaling treatment, but I've not heard of the same with standard pipes. If they were quickly descaled, there might be a large amount of debris, which would necessitate disassembly (washer inlet filters, refrigerator water connections, shower valves, toilet valves). Perhaps all the hose hookup devices could be disconnected for the treatment

It's likely that the type of meter you have is called a PD meter.

PD Meters are very accurate, but do this at the expense of pressure.

My guess is that increasing the volume of the meter likely does do a little to reduce pressure drop. However, without the actual specs for each meter, it's impossible to say how much.

That said, **it is highly unlikely that a 2" meter in the middle of a 1" line it's making a $1000 (or even $400) per year difference in pressue. For less than $1000 you can can make a one time investment in a residential pressure booster.