I did go for cellular in the end and am very glad I did! I forgot an important piece of paper this morning. While I was in the train station, I was able to turn on my cellular, download the document from an email, send it to Notability, and then edit it on the train.
Even though it's a tiny thing, that convenience was worth the extra cost for me! I was able to reclaim my day and not need to stress about being forgetful. Of course I could have tethered from my phone, but I always forget that I can and there's a lot of singing and dancing and juggling multiple devices that wouldn't have been easy standing in a queue on the platform.
I really spent days and days agonising over whether to save the money or not and am really grateful I went with my gut in the end.