Gifting is supposed to be fun, so I don't feel like I can say: "I really don't like Star Wars anymore, so this extremely expensive item is wasted on me" or "This item is too large for my flat" without sounding ungrateful.
I agree with this, but with one caveat: Gifting is supposed to be fun, but so is getting a gift! Unlike OldPadawan, I would advise against trying to solve this the moment you get the gift, or shortly after. Also, if you joke about it, you're not likely to be taken as serious, and to me it seems you need your family to take you more seriously.
What has worked for me in the past is being blunt, but doing so before the gifts are bought. I've even included an ultimatum like "I won't use those gifts and will have to gift them to others or put them in the trash barely used."
As an example, a quite acceptable small gift you'll get from family and friends for a birthday is those gift packs with shower gel, deodorant, and body lotion. Except: I have a sensitive skin and over the years, it seems to have gotten worse. Some brands that I could use years ago now trigger rashes and itching. So, what used to be acceptable gifts for me are now no longer working, and I resorted to extending the invitations to my birthday, with a very blunt remark about how perfumed or soapy gifts weren't going to be used.
Close family can help spread this message to more extended family, for example my mother used to handle the 'guest list' with extended family members and helped spread the message to them. She also helped to reinforce the message to the people I already spoke to.
I think you can be more blunt than sharing your reading list. You should explicitly mention that your love for Star Wars is over, and put out an ultimatum: any Star Wars themed gifts this year will end up at the charity shop unopened and unused.
If after that they still do gift you Star Wars themed gifts, then it's really their fault their money is wasted. At that point, I wouldn't feel too bad reminding them that you are disappointed as you specifically asked for 'No Star Wars', no matter how rude that may seem... it was kinda rude of them to ignore your wishes too! Again though, don't joke, you want to be taken seriously! A gentle but serious reminder should work, something like "I'm sorry, I thought I mentioned specifically that I no longer needed Star Wars themed gifts". In my case, this worked and the family member that gifted me soap admitted they forgot, and at the same time offered to take the gift back to the shop and get me something more appropriate. *
* In the Netherlands, it's quite okay to take a gift back to the shop. If someone has a wish list with e.g. household items, it's prudent to keep the receipt and if e.g. the color of the item isn't okay, the host of the party can be honest and I will promise to switch the items for a correct color. This also goes for e.g. items that are damaged or that don't work as expected: be prepared for your party-thrower to ask you if you kept the receipt and could help them with returns. This may be a bit more blunt than in the UK, so perhaps you can't expect the same offer... hence the footnote.