Lately I've been shooting kids birthdays... nothing paid, just for friends, but as people like the photos I take, I get invited to do more... maybe I'll get paid at some point, which would be nice as it would finance some LBA...
But as I build my system, I can't think of maintaining two systems. If I thought something like Nikon FF would give me a better return, I'd go fully Nikon and leave Pentax. So far, I think the value of Pentax is far greater than a Nikon system would provide to me. And I love the look of some of my lenses.
1. A full frame Nikon system would give me an extra stop of light (compared to something like a K-3, K-5 or K-50). But I shoot these events with flash anyway.
2. The full frame system would give me a narrower DOF. That would be helpful in some cases (taking pictures of the arrangements and such) but a 50mm f/1.2 would probably be all I need in that contest, if I were looking for narrow DOF. I actually make do with my 50 1.7 currently and I've had no complains...
3. A full frame system would provide the correct view for normal and wide angle pictures - meaning that the background wouldn't be diminished and the foreground wouldn't be over-emphasized. I love my 35mm f2.4 and use it as my "normal" lens, even for event portraits - these kids parties are usually pretty crammed - but being able to use a 50mm on FF would certainly make the images look a bit different. For birthday parties it's not an issue as there isn't a deep background usually - it's just indoors stuff. But if I were shooting environmental portraits, as often is the case with weddings, FF would definitely have to be a consideration.
So to explain this - I would imagine that if you shoot weddings at country clubs and other outside venues, having a proper view of the background would be key. A 50mm lens might be a bit long for a full body portrait, but it would be the minimum necessary to keep the proper background view. 70-77mm would be ideal (I've been using my 70-210 more and more for portraits - I LOVE how it looks - but I need a lot of space to take the shots...). Of course you could always step back and use these longer lens for the full body portraits - outdoor venues would probably give you that option - but ideally the format would let you stay reasonably close and still get the proper perspective of the background. Sometimes you don't know for sure that you will have the proper space! And couples rent places with a nice view because they want that as part of their album - and they don't want that view to look like it's much further back, or much smaller than it really is
So while my points 1 and 2 would not make me consider a move to full frame, I think point 3 would. Right now it's not a necessity for me (I'm making do with what I got), but it might be for you, depending on where you are shooting your weddings.