Aww, Jimbo, I'm sorry your Father's Day outing was half-disappointing. Our experience at Bletchley was different to yours. It wasn't particularly busy on the day we went (in September, 2016), so we were able to get up close to view everything. I feel like I remember one or two school groups there... something was going on that let us get more information than just wandering around would've given.
We also went up to see the computer museum after our mostly self-guided tour of Bletchley, but we left it too late and the museum closed just before we got there. However, one of those enthusiastic people you mentioned saw us peering in through the windows and she brought us into the Tunny and the Colossus Galleries to show us those computers. She gave us a lovely talk about them and powered up the one in the Tunny gallery. It was lovely of her, and fascinating. I'm sorry we didn't get to see the PC Gallery, or some of the other stuff, but what we were shown was interesting, and it was more than we deserved, since we were there after closing time!
On our same trip up that way (the day before Bletchley), we also went to the Imperial War Museum - Duxford (about 50 miles east of Bletchley), where they have a decommissioned Concorde, an American B-52 (*sigh*), and a bunch of other interesting aircraft. All in all, it was a very enjoyable weekend that involved a LOT of walking... but still very enjoyable, nonetheless *emphatic nod*. Plus, after the IWM, we followed the advice of some TripAdvisor reviews and discovered an out-of-the-way pub called
The John Barleycorn near Duxford that was
amazing.
I wasn't driving back then, so I did not notice anything to do with roundabouts.