I finished New Beginning and No Quest for the Weary both at platinum level.
For No Quest for the Weary I tried to minimize the number of 4QP quests I did to ensure that I was able to complete >16 quests with the 60QP available. Even with 1 bugged quest that I had to drop and 1 quest completed at gold, I was easily able to complete something like 18 quests at platinum.
One strategy, which I didn't use but could be helpful if you have difficulty completing quests at platinum consistently, is to annex the territory that gives the benefit of decreasing quest costs by 1 QP as soon as you have the opportunity to do so. I forget which territory it is, but I know there is info in the guide about it. This will make your QP go even further.
I am really getting bored with my second ambition. I completed New Beginnings at Platinum, it was great. But this one (Imperial Domination), is repeating the same quests all over again. I don't understand why I had to do the Missing Child quest three times so far.
The game does get pretty repetetive after a couple of ambitions. There is a finite number of quests so there is really no way to avoid repeating them over and over again. What I try to do to not get bored is use different heroes and approaches to see how they play out. I also try to focus on different heroes to make sure I will see every class at maximum level eventually. I think even that strategy will be tapped out long before I complete all the ambitions, though. I would assume that EA is going to add content over time or else TSM will have a limited lifespan.