Not recommended, even for Kairon.
Nintendo has done a good job so far with providing value with their downloadable expansions for software. The Mario Kart and Hyrule Warriors DLC packs are filled with good content (depending on your threshold for Tingle and Baby Park). Then there's the recent update for the StreetPass Mii Plaza, which adds a few extra bits of customization but also adds an upsell for the new StreetPass Premium service. The premium service really only has one feature worth your money, but that’s not enough to warrant the $4.99 price tag (or $6.29 one in Canada).
The most prominent added features are the three on the main menu. You can save up to 100 Miis in a VIP Room, which might be nice if you want to preserve the likes of Abe Lincoln or Reggie for posterity, but those special Miis come out often enough – especially for the Nintendo executives – that they're not going to get scrolled out of the plaza unless you go to PAX every weekend. You can't even call them up in StreetPass games on demand. Admittedly, that would break the games if you did it with the special Miis, but at least it would justify VIP storage.
For Premium members, the music player in the StreetPass Mii Plaza features additional support for listening to music with the system closed. Unless you really love yourself some StreetPass Plaza music, you won't use this feature at all; if I'm going to boot a 3DS game to listen to music, I'll be firing up Theatrhythm Curtain Call and blasting some quality Chrono Trigger music.
The final major feature is the addition of birthday tracking for Miis, which is tied to a round of plaza tickets. If you're obsessed with collecting all of the hats and newly added speech balloons, you'll have to buy Premium to get them all. Sorry about that. The Miis have always recorded the birthdays, so it's nice to see a use for it, but tying tickets to it to force the obsessives to buy it is not cool.
Ironically, the most useful features for the StreetPass aficionado aren't in the main menu at all, but hidden away in the settings menu. The ability to disable your choice of things during the StreetPass conversation is useful if you're rapid-firing at a convention, for instance. Although I personally wouldn't turn off the game intros unless I found 10 people in a row playing 3D Classics Urban Champion. It's a shame that this part's locked behind a wall of useless stuff.
Would I have paid for these features in the collective? Maybe a buck for conversation skipping, but certainly not a fiver. Could the rest of the “additions” have been left out and the conversation settings included with the Battleground Z and Ultimate Angler update? That would have been the ideal solution, since as it stands right now it seems Nintendo is trying to get people to pay to stop menu nagging. And that's never a good thing.
What would have been worth it for five bucks? The biggest thing is expanded storage for Miis. Ideally, we'd have no limits on the number of Miis that can be at the gate at one time – the games would have a 10-at-a-time restriction, but the plaza itself could have unlimited. The other big thing I want and may pay for involves the two empty slots on the game list – early access to future StreetPass games. If they came out on a Thursday again, Premium members would get it on Monday. In combination, that's an attractive feature set for five bucks.