I've actually just checked the Central British Roads Database's
A1 pages. There are in fact only five roundabouts on the A1, but they're all on the section I use the most, Baldock to Alconbury. They are at Perry, the notorious Black Cat, Sandy, Biggleswade North and Biggleswade South. That's actually parallelled by
two motorways, the M1 and the M11. There are also five T-junctions where you can cross on the flat, and three where you can't on that section alone, and a total of thirty-three on the entire road between South Mimms and Washington.
So, yes, the A1 has seen minor tweaks along its entire length. What they have been doing is patch-fixing difficult sections rather than miles and miles of plain road. The major exception to this is Yorkshire, where they decided to sort it out properly. The second short exception to this is the hugely-overblown section between Huntingdon and Peterborough, which also includes the A14-A605 link (a major E-W link). IIRC, originally, that would have run all the way to Baldock, but it got cut back. Interestingly, that's the bit that runs through Bedfordshire, although I can't say whether this is the reason. Of course, it's always worth a closer inspection of some of the patch-fixes (q.v.
CBRD Bad Junctions - the A1 has five all of its own, and they really ought to add Letchworth Gate as a sixth).
So, it may be that I ought to blame the counties rather than the M1, since Bedfordshire, Lincolnshire and County Durham seem to have done far less than Yorkshire or Cambridgeshire. Hertfordshire started off OK, but stagnated, with no improvements since 1986. However, you ought to look more closely at CP5. What is the overall outcome of everything that goes into it? Is is there to promote the growth of long-distance traffic on routes parallel with HS2, or is it there to promote local traffic on those routes?
What really concerns me is not CP5, or indeed anything in the next two decades, it's whether I'll still be able to get to Aberdeen with one change in 2050; whether the train I'll be travelling on will be as good as or better than an IC225; and whether the journey time will be faster or slower.