What's the minimum you can spend on your card on the eShop again?
Normally, if you have a positive balance, you don't have to put £5 or £10 on -- you can just pay the remainder of the cost of the game...
so if I had £6.50 or something on my balance and the game was £6.99, could I just pay the 49p on my card? I'd imagine either Nintendo or us have some kind of transaction fee to pay?
I noticed a "Earn points on all digital purchases made through Dec 2014.
Exchange points to receive activation codes by Mar 2015." under Promotion.
What does this mean? Get the codes after 2015 or up until? And why this cut off, why not the entire life cycle of the system?
It means games will only get you new codes until the end of 2014 (unless they extend the scheme, which they might if WiiU is doing well)... but you can still exchange your existing points and spend them on the store until March 2015.
So wait, how do I do this? I got the deluxe version, but haven't purchased anything from the eshop yet. I'm planning on getting NSMBU soon as well as Nano Ass. and Trine 2. What do I do and how much will I save/redeem?
It's 10%. So Mario at £42 gets you 420 points, Sonic Racing at £33 gets you ~330 points, Puddle at £6 gets you 60 points etc. It's fully automatic providing you registered your NNID on the premium system. Just go to ddp.nintendo.com and login with your NNID after you've made some purchases, and each time you get 500 points you get £5 back. (or €/$)