As such, this console might just pass the old 'you should want games costing more than the console itself' test. I already own a PS4 and Xbox One. As it stands I have insufficient time to play games for my existing consoles, letalone consoles from last generation (got them all) or Steam. So there is no pretending I need a Wii U. Also have a 3DS.

So I have a couple of questions.  

1. What features do I literally miss out on by having a Basic instead of a Premium?  Feel free to list obvious and more nuanced ones.
There's only 8GB of memory on the basic, as opposed to 32GB on the Premium. Either system can be used with an external HDD, so if you have one lying around great. If not, and if you are likely to download a lot of software, then you'd need to consider the extra cost of an external HDD. You'll also miss out on the Nintendo Network Premium discount, whereby you get 8% cashback off every eShop purchase. 

2. Are there games you feel I should definitely be considering (I enjoy very high production value platformers like Mario or Banjo Kazooie)? Realistically I'm likely to leave racing games and shooters to the consoles with more power.
Donkey Kong: Tropical Freeze, Super Mario 3D World, Rayman Legends if you didn't play it on other formats. Though you say you'd skip Mario Kart 8, I would highly recommend it. Kart is normally a franchise I would buy as a party game, to use when other people are over. Kart 8 is keeping me thoroughly entertained because it's a superbly balanced racing game with insanely high production values; quite clearly the best Kart yet for my money. I'd also recommend Pikmin 3, Wind Waker HD, ZombiU (it should be dirt cheap) and Wonderful 101.

3. Any other factors that could or should influence my thought process on this?
Are you going to have the time and money to keep on top of all the titles you want to buy? Are there enough titles to make the Wii U useful as a machine you use occassionally? I bought a Wii U thinking it would be my secondary console, that it would only keep me busy for a few months before I got a PS4/Xbox One/gaming PC, but Wii U is going to keep me busy into 2015. I'd also say Wii U, out of every console on the market, offers and will offer the most unique experiences when it comes to retail software. The future line up of Hyrule Warriors, Bayonetta 2, Captain Toad, Smash Brothers, Xenoblade Chronicles X, Mario Maker, Splatoon, Star Fox, Yoshi, Kirby, Zelda is eclectic, and unlike anything other formats will give you access too. If you're a multi-format gamer, Wii U is worth it on the strength of its exclusive software alone, though an increasingly improving eShop, backwards compatibility with the Wii (digital and retail, meaning I can finally get around to No More Heroes 2 this year), and hopefully an improving Virtual Console are all strengths in the systems favour.

4. Though I cannot imagine a price close to this anytime soon, is there some sort of price drop speculation of note that could lead to a lower price of entry in future?
I know nothing about this, but the price you have here seems very cheap.

5. Are there accessories or things I will require not factored into the price?
Extra remotes etc, possibly. A pro controller if you are so inclined, I haven't found it necessary; the gamepad is a good controller and surprisingly light and comfortable.

I really do welcome opinions on both sides of the argument - I concede of all next generation consoles I am least knowledgable about the Wii U, beyond knowing it has some fantastic exclusives already.