Thanks everyone for taking the time to post all that.
Dave, I'm happy to spend the extra $80 to get a much better radio, if that is indeed the case. I do have radios for the other digital modes, so no hotspot needed. Hotspots are also something I haven't investigated yet, and I really don't know much about them. More reading for me.
Vagrant, now I remember reading about the X model being newer/better (I had read the 400 reviews a year ago). I prefer buying new in this case, for warranty purposes.
W9BU, I hadn't really thought about the 400 potentially being near EOL (good point), but rather was thinking that since the 300 was shiny and new, maybe it was using more modern tech.
Mrweather, that's likely where mine would come from (or from their Calgary location). Unfortunately my local store is not a Yaesu dealer, as I prefer shopping local. Stock difficulties just means more time to research the two units, plus I'm not in a hurry (I don't "need" another radio).
Chief, I too have experienced the annoying "minimum volume" issue, especially with LMR and during late-night sessions. Glad that's not the case with either unit.
I actually prefer a non touch screen generally; I'm one of those people who think that radio displays are meant to be seen and not touched (I hate fingerprints and micro-scratches on displays). I've always thought the 400 screen appeared to look overly big in the photos, but I've never seen either radio in person. I would really like to compare them though, before discovering too late that the 300 display is indeed too small for me.
I know I didn't ask, but nobody mentioned anything about packet capabilities, which is another thing I've not investigated yet, but was hoping to with this radio, rather than having to buy a modem and interface it to one of my existing radios.