Good write up. I agree on the XP boost value. Personally, I have several and it has sped up my levels considerably. I think 20 hive is VERY worth it. They are limited and discontinued, so one could easily buy one to use for awhile, and then sell it later for likely the same or higher price. However, I think it would be hard to sell, once you see the difference. Would be like getting off the highway, and driving super slow in traffic.
The birthday cakes are useful, of course, but they are super rare and very collectable. I own one as a rare collectable NFT, and also get to use it everyday.