Speaking as somebody who has been at Chiltern since Warwick Parkway opened, Warwick has always been the quietest of the three stations in that area (there is barely three miles between Warwick Parkway, Warwick & Leamington Spa) and people in Warwick tend to use either Parkway or Leamington Spa stations, maybe because car parking at Warwick is very limited and the services arent a patch on nearby Leamington Spa.
Looking at the passenger numbers I am genuinely surprised to see Warwick Parkway and Warwick get quite similar numbers. I would wager that the bulk of people travelling into Birmingham or London use Parkway though, Warwick is a place where a lot of people from outside the area travelling in will get off (either to visit the castle or use the nearby hospital) and the locals tend to use the station a lot just to get to Leamington Spa. I think Chiltern are making a good call with what they are doing to Warwick, it should benefit the majority of passengers.
High Wycombe is another one. I dont know what the breakdown of tickets sold at that station is, but I wouldnt be surprised if well over 90% of them were for London or stations between Wycombe and London. There appears to be a semi reasonable amount of travel between High Wycombe and Aylesbury, and I would think that when Oxford opens there will be a fairly significant number of people travelling between those two towns, but the numbers of people who travel between Wycombe and Birmingham appears to be quite low. I wonder how many season tickets between the two places get sold? I'd think its not very many at all. Chiltern's core is getting people to London. The Birmingham commute really only exists from Leamington Spa northwards, arguably Banbury northwards I guess, but not beyond that.