I had two UY's for a very short time and I didn't like it. But, I also only had 50 points in one of them and that made it more difficult.
When you have 2 UY's, it is two different memberships. That means you can not combine points for a single nights reservation without using up your once per UY transfer.
So, in my case, I had a 130 points in one UY and 50 in the other. To book my typical 5 or 6 nights a year, I didn't have enough points to do it without borrowing, something I did not want to do.
Now, if the contracts had enough points to achieve what you want and you plan to use them for different vacations, it might be easier to manage.
IMO, it's not worth it to have two memberships.