If you intend to use these yourself combining them to get a vacation, it makes sense to get them on the same use year, same contract. If you would tend to use them separately, then I wouldn't see as much an obstacle, maybe even a slight benefit. Like say you wanted points at BLT and at BWV, and you intended to take trips to BLT in June and BWV in December, then it would be fine to get a BLT June UY and a BWV Dec UY because you're not mixing the points in general. If you only own BWV and you're buying additional BWV, I would only consider matching up the UY. Otherwise you'll have fewer points on each contract which will limit the amount of days you can book on any one contract... Like if you can only book 4 days on each contract, then you are missing the benefit of being able to book your arrival date +8. You'd be booking arrival +4 and then another arrival +4, later on the other contract. Having the bigger pool of points will be easier in every way for playing around w sandbox reservations.
Yes you can transfer one to the other, but even that is not great. You can do it once per UY (which in itself is fine, cuz you just transfer them all and you're done) but you can only transfer current points, so you still can't get the full flexibility that you can if you had them all in one account where you'd have access to all of your bank and borrow options. Then transferred points won't show up in your online view, so you have to call member services for every res instead of using the online tools and seeing all your points.
Waitlisting w a split / linked res would be a nightmare. You'd have to waitlist on both accounts, and hope that one doesn't score and the other fail, or you'd have yourself a mess.
For all these reasons, if you're matching the resort you already have, I'd pay more to get the UY to match up too.