One thing to watch out for, especially in the Northern PTE areas is that Plusbus tickets are only available with train tickets to or from certain stations within the zone. For example, travelling from Manchester/Rochdale into West Yorkshire, the first station at which Plusbus is available is Halifax, even though a Halifax Plusbus ticket is available throughout West Yorkshire - even on those buses running near the train stations in Todmorden and Hebden Bridge. So if I want a day out in Haworth, it's either a train ticket to Halifax and a Plusbus (even though I'm only getting the train as far as Hebden Bridge) or a train ticket to Hebden Bridge and a K-Day ticket for the Transdev Keighley bus to Haworth, which I think works out slightly cheaper, but doesn't give you the flexibility of being able to use WY's other buses later in the day.
I think Plusbus should be available with trains tickets to/from ANY station in the bus validity area. It would be a lot easier to use if that were the case.
Peak District Plusbus is another example - available only with train tickets to/from a handful of stations, but not Hope or Bamford, both served by buses and really useful for daytrippers from the Manchester direction. OK, people from GM can use the excellent integrated TfGM Wayfarer ticket, but what if someone's travelling from further afield and also wants to use the bus from a station in the Plusbus zone, but not a designated Plusbus station?