It sounds like a great idea, include the area where you can see the famous university buildings from a public place, except it's actually very limited in terms of what you do see.
The only way to properly see the famous college backs is to pay for a punt, either as part of a group or, if you're feeling adventurous and don't mind the thought of falling in the River Cam, hire one to take out yourself.
The problem with both these options is they are not free, they are worthwhile, I've done it twice but you really need a nice day and it's advised to arrive early during peak times and holidays.
The best sight from the punt is The Bridge of Sighs and that is one of the sights you don't see from the footpath that follows the backs.
Don't misunderstand me, you still get a magnificent view of Kings College Chapel (picture) and St John's College but the views to many sights are limited.
For that reason alone I agree with UNESCO's decision not to award a full listing.
On my many visits to Cambridge I have been to a lot of the various campuses, my philosophy is to saunter in for a nose around and leave if I'm told to.
Playing dumb often pays dividends.