What was the service from Huntingdon and St Ives to Cambridge like before the busway?
The long standing Hunts & District Service was broadly three buses an hour (with peak extras) that had three slightly different routes between St Ives and Huntingdon (553, 554, 555). (Wyton Airfield and Houghton village were both served broadly hourly, and the services that went to neither also took a direct route though Huntingdon rather than a different and more thorough route through Oxmoor than offered presently). The fastest of those routes was timetabled to be 55m off peak, and the slowest rush hour journey was timetabled to be 80m. In reality none of these timings were ever met except late at night, and of course when the A14 had a hissy fit they would be missed by a tremendous amount! The H&D service was broadly hourly in the evening and they did not operate a Sunday service. For a long time there were two additional M-Sa subsidised evening service 151s from Cambridge that served Oakington, Bar Hill, Fen Drayton and Godmanchester (one return).
H&D also had a daily X14 to CRC and the Science Park. It went via Bar Hill direct to the Science Park and was timetabled to take 90m.
A typical timetable can be seen at
https://web.archive.org/web/20060112032246/http://www.huntsbus.co.uk/hd553mh.html , but it's worth drawing attention again to the fact that those timings were never ever met except in the evening. I typically used the 0620 and it typically took 70-75m. I tried to take it as even the next bus was much MUCH slower!
It's worth mentioning that all did not seem to be well at Hunts & District in their final years or so. You would previously have expected to travel in a perfectly respectable Wright Renown, and there was also an Optare Excell. Towards the end some truly dilapidated ancient Leyland Olympians seemd to be more in charge.
Whippet timetables were subject to more tinkering. There were routes 1A and 5 between (usually) Huntingdon and Cambridge(with an additional call at Bar Hill Tesco that H&D didn't offer), and there was a route 1 that was (usually) between Cambridge, Cambourne & St Ives. They combined such that there was a broadly hourly services Cambridge - Cambourne - St Ives, and slightly more than hourly Cambridge - St Ives - (More of St Ives than H&D, or Hemingford / Godmanchester) buses. Whippet did not run in the evening during the week, but did run a Sunday service that for a while extended to Peterborough and that for a while ran in the evening. Towards the end it was an hourly daytime service between Huntingdon and Cambridge.
Whippet's fleet was typically very much older than Hunts & Districts, but always very very VERY smartly presented.
For wayback machine purposes Whippet's website used to be go-whippet.co.uk, but it doesn't work well.
I'm assuming that the main services ran via A14 –
Almost exclusively they were. Quirks of Whippet's very excellent and comprehensive timetable planning, that really got the most out a fairly diverse network that also served a lot of villages at least every couple of hours, was that the fastest journey time was in fact on a Whippet bus via Cambourne that at the time only ran once during the middle of the day. Similarly, today the fastest journey time is Whippet's X3 on a broadly similar route, but now operating more frequently.
has the busway sped journeys up by much
I would say that the busway probably did not speed journeys up (by timetable they are slower but in reality probably they were about the same, except in the evening when they are slower), but it made the journey times massively more predictable.
has the frequency improved significantly (at least, up until the end of 2019)?
This is where the really rather stunning improvements were to be found.
By the end of 2019 St Ives was seeing 8+ buses an hour instead of 4-5, and the Sunday service was varying between 3 and 4 buses an hour (depending on the timetable) instead of 1. Evening services were roughly doubled. I don't think there is anywhere else in the country where this happened during what was a period of decline for buses in general.
In early 2020 there was a large publicity drive for a massive relaunch with some incredible service improvements that were to take place from the end of March (leaflet attached). We all know that of course something quite different happened in March 2020.