I have exeperienced the bar, and would rather it was not there, but I like the IETs on GWR. Those are the only ones I have used because of my location. There would be no problem at all with CrossCountry ordering IETs in my opinion.
That said, I also like the voyagers (though occasionally wish they were longer, I never seem to get them when they are completely full),
I had not thought about the dwell time effect of making carriages longer. Silly really because clearly more seats means more time to get on/off through the same number of doors. However, if IETs are only running true limited stop routes then dwell is less of an issue. In GWR land things are a bit different because IETs become regular stoppers for parts of their journeys.
I do have a nostalgic view of the old Mk3s on the MML (less so when I moved to Manchester and was a regular on the WCML), and of the introduction of the Mk4s on the ECML. However, as others noted the rennovations did little for the Mk3 and though CrossCountry were ok in the final years, I was not a massive fan of the GWR ones. The Mk4s meanwhile are tired now and have limited value away from the ECML. Even the retirement main line of London to Norwich is not available for Mk4s any more.