In my current save, I've had a sim go from living in a trailer because she couldn't afford a proper home to having so much money she never needed to work again (not a million, but then I never strived for that). I have had her daughter cope with 5 kids, 3 of which were toddlers at the same time and all of them getting the #top notch toddler" reward. As her husband was cheating on her she had a very messy divorce but has now found love again and remarried her "soulmate".
In other words, I have in one save done two out of three challenges and sort of the first as well, without running a single scenario. For me, the fact that I cannot run them on existing saves is a major flaw. Other than that - I agree wholeheartedly with the first post as well as with wishes for customization.