...the poor UY months for frequent June travel dates would be July-October, since the Rule of Four would be in effect for June with these use years. If you had to cancel a June trip and you had a December UY, you could still bank the points or use them in other collections, since June is the 7th month in this UY period. Thus, December is fine (barely).
The easy way to determine the if the travel dates are affected by the Rule of Four, just take the four months following the travel month. If your UY is one of these, be cautious about canceling or waiting to book in a Collection.
Personally, I would think the hardest part about managing two UY would be keeping the member numbers straight.

Although, you may be able to get some benefits, such as a promotion that is "one per member", having each spouse manage a separate (their own) account, splitting the DVC membership between children (they can't undercut each other if they both have separate accounts), and possibly others.
I do caution; however, about making a decision based on "we don't plan to do X or we won't need to do Y". Murphy's Law will come along and make sure you need to do both X and Y...at the same time...frequently
Good luck!