I don't agree. Part of the reason why BHX merged both their former T1 and T2 (Eurohub) facilities together was to realize the benefits of a single passenger throughput. Not only can it make core operational processes more efficient, it allows every passenger to get the full "experience" thus maximizing consumer choice, and that's only getting more important as airports diversify their income.
There is of course merit in that concept. However, it brings us back to where we started, that BHX no longer has the infrastructure to provide this single passenger throughput. Consequently I question its "efficiency". As for spending money in the terminal, last time I departed from Brum I wanted to have a hot meal at G's (this around 3PM in the afternoon on a Thursday). I was told it would be a 45 minute wait to get a table! I didn't bother. Had a coffee at Costa's and bought food on the flight!