Personally I think adding Trent Valley calls to Virgin services is a retrograde step, and that attention should instead be focussed on improving the London Midland service, such as: (i) running from Stafford to Crewe non-stop, to improve connections at Crewe; (ii) improving the quality of the accommodation, such as plug sockets throughout, a trolley service and better first class accommodation (which seems to be a frequent gripe of Lichfield passengers); and (iii) 12 car running throughout most of the day (which would be an easier alternative to the option of upgrading the service to half hourly).
Virgin services are already, for the most part, very busy. Adding additional intermediate stops south of Stafford: (i) reduces revenue, as passengers travelling from, for example, London to Lichfield will not be paying anywhere near as much as passengers travelling from London to Manchester, but will not be replaced to any significant extent by passengers travelling from Lichfield to Manchester; and (ii) slows the services down, lowering their flagship status, and even having an impact on services whose calling pattern remains unchanged (e.g. the 08:15 from Manchester is having its arrival time in Euston extended by 6 minutes to enable the 07:55 to call at Lichfield and Tamworth, and I wouldn't be surprised if it ended up regularly grinding to a half somewhere along the Trent Valley to allow the 07:55 to maintain its path).
On the Manchester route (e.g. the 19:40 Euston to Manchester), the vast, vast majority of passengers are on the train for the whole distance to Stockport / Manchester, especially in first class. I'm less sure about the southbound morning services and the 16:57 and 17:57 northbound services (via Warrington), but there is a clear contrast with London Midland services where the vast, vast majority of passengers from London alight the train by Lichfield.
If Virgin introduced a second hourly Liverpool to London service to call at Lichfield and Tamworth, where else would it call? Nuneaton, almost certainly. And how about Milton Keynes? Milton Keynes is a major employment hub. It would make little sense not to connect Milton Keynes with Nuneaton, Tamworth and Lichfield. That leaves Rugby, which could perhaps be skipped, but the Rugby Rail Users Group would have something to say about that, particularly as Rugby only has an hourly fast service to Milton Keynes at present. At this rate, the Virgin service will end up being only 5 or 10 minutes faster than the London Midland service, and with the existing hourly Liverpool service just behind! What is the value of using expensive 390s on this route over more affordable, more flexible (4, 8, 12 car), high specification 350s, which in turn permit more affordable fares?