I think the Lego designers based the UCS set on one of the original scale models used in the A New Hope. There is one so called "superhero model", which is an incredibly detailed model used for close up shots. This model has battle damage and oxidation, both of which are very hard to replicate using Lego bricks (except when using prints or stickers). Another thing is that the scale of the UCS model is a bit off on some of the parts. Namely the tubing is way too thick compared to the rest of the model. The actual model has thin copper tubes, which don't stand out as much (they are more of a yellowish copper).
Now all of this is about the original model used in A New Hope. It was given to someone named Alan Jadd who helped Lucas get his movie released. It looks like this:
More pictures over here: https://propstore.com/blog/top-5-star-wars-artefacts-in-prop-store-ceo-stephens-personal-collection/
From what I've read there is a LOT of difference between different models used and especially between different films. One good example is this model:
This model was made by Bill George (ILM) and if I understand it correctly, was used in Return of the Jedi. More pictures here: http://www.modelermagic.com/?p=2722
Now the pictures are kind of dark, but it's pretty clear that the copper tubing is way less pronounced on this model. It's very thin (which is not possible to replicate in Lego unless you change scale) and the colors are more muted.
Here's an interesting video about the background behind the original superhero y-wing model:
As you can probably tell I'm a big fan of the Y-Wing. I can understand why some people might not think much of it, but to me it's appearance fits perfectly with the role it has to play in the rebellion. I think the line Luke has about the Falcon, fits the Y-Wing just as well. It might look like a piece of junk, but it'll kick your a** any day.