We see the 30% Bonus as being of value only if we can use the residual.
E.g. If I book something for 3000 and within 60-Days Cancel + Rebook for 2100, I am left with 900 Restricted-Points unless I increase the #-Days for the stay. However, this is not easy with airfare already booked and other plans.
Yes, it depends where you go and how many times. Being that I traveled over 90 nights last year, it was trivial to use the holding account points. As you said, we have never used them to extend the trip we cancelled and rebooked for as there are other plans in place.
There are several ways to rebook. Safest is to start a points reservation (it's now on hold) then cancel, then complete the on hold one. In this manner, you are only left with 30% holding account points instead of all of them.
We simply use them at the next stay, or, in Branson virtually any time of year.
If it's past July, we borrow the points to make the reservation. So, for a August 2021 reservation being made in August 2020, we'd use 2022 points. That way, when we cancel and rebook, they are holding account points we have all of 2022 to use. But we've never come close to not being able to use them. There are so many places you can book within 60 days in any given year. But, if you are tied to a school schedule, it's much harder indeed. Definitely not for everyone.
I have a spreadsheet of sightings by month for within 30 day bookings (executive), didn't keep one for within 60 days (presidential). Minimum was 1BR, i.e. didn't count studios. Over the course of a year, there was within 30 day availability for at least one full week for:
All Palm Desert
All Lake Tahoe, including Ritz
All Colorado including Ritz
All South Carolina
In short, virtually every MVCI was available at one point in the year within 30 days of reservation. So, if you are very flexible, it's trivial to use those holding account points. Obviously, not all of these are high season, but many are. You'd be very surprised unless you watch it daily. Honestly, I was shocked as I didn't think it would turn out that way. This was done 2 years ago before any virus impacts;.