Hi,
we booked our split stay 4 day
dcl cruise and 6 nights at POFQ for this december through Virgin. We had to book it through Virgin Cruises rather than Virgin holidays. We booked a year out and chose to book the package as we are travelling over Christmas and, as a teacher, I am very restricted for flights and I wanted to be sure to get on one and flights weren't on sale at the time! For us, travelling at that time of year, the price was very competitive (very expensive but very competitive and hey, we will be in the bahamas on Christmas day!) and I couldn't get it cheaper by booking elements separately either then or looking since.
However, if it had not been peak season, and having spent hours on here since, I would probably opt to book it all separately. The benefits of having a TA (esp a US one) for the cruise element is the on-board credit they offer. We got nothing from Virgin, although they did offer it as an incentive for all other dates than Christmas.
I have also found it very restrictive having to go through Virgin for any correspondence or ammendments I need to make, a) they try to charge you for any changes, far more than Disney do. b) they really don't have any knowledge of DCL and how it works beyond what is on their screen so I think a US specialist for DCL would know a lot more (as do people on here!). I have ended up telling Virgin many things that I think they should have told ME about eg wait listing for dinner sittings etc
I also was limited to the cabins I could choose (as in specific cabins) as Virgin had obviously only block booked certain ones and I had the same trouble not being able to get our first preference for room type at POFQ, even though the Disney site still had them as available.
I don't know if that helps at all!

I would definitely price it up both ways. I don't think a TA in the UK gives you anything extra other than simply doing the bookings for you, which I'm sure you can do whereas I have heard that US TAs seem to go above and beyone a lot more!