These amiibo never really interested me when they first came out, but at some point I finally got taken by the hype and tried one out. My collector's OCD quickly kicked in and here I am now trying to collect them all.
It took me awhile to figure out how they actually work, so hopefully I can help others make sense of it all. First of all, if you want to actually use them, and not just collect them, you'll need to take them out of the box because there is a metal square in the packaging that prevents the NFC chip from being read through the packaging. Curse you, Nintendo! You'll also need an amiibo-compatible game and console.
*Kirby*
Here is Kirby's current compatibility across amiibo-enabled Wii U/3DS games:
Super Smash Bros. (Wii U/3DS) - Read+write - Train and fight your amiibo to level it up, each battle your amiibo is in earns you extra coins & items.
Mario Kart 8 - Read only - Tap once to permanently unlock a Kirby outfit for use while playing as your Mii character.
Hyrule Warriors - Read only - Tap once per day to get a weapon rated 3 stars or lower, or rupee/crafting material bonus.
Captain Toad: Treasure Tracker - To be announced
Mario Party 10 - To be announced
Kirby and the Rainbow Curse - To be announced
Yoshi's Woolly World - To be announced
*Read/write*
It's important to understand how these work. You can save data from an amiibo-compatible game to your amiibo figure itself. But you can only save one game data to it. At the moment, the only game that actually writes to amiibo is Smash Bros. The other games just read from it to unlock items without saving anything back to the amiibo. But as more read+write games come out, you will have to decide which game to tie your amiibo to. You can always delete the data on your amiibo, so if you change your mind on which game to use it for, it's not a big deal. You will just need to wipe it clean and start over. For read-only games, you can use the amiibo to full effect while it is storing data for another game. For example, all my amiibo have Smash Bros data saved to them, but I could also still use them afterwards for unlocking Mario Kart 8 outfits.
*Quality*
These are actually very impressive quality-wise. They have very detailed molding and painting and are really not a bad deal for $12.99. Some of them come with some imperfections, however. My Samus has a side-leaning stance that looks kind of stupid, and Link has a bent sword, ha. But for the most part, they look fantastic.
*Rarity*
Unfortunately, it appears some amiibo quickly ceased production, though this was never officially confirmed by Nintendo. Unless they decide to make another run of older amiibo, this leaves some of them being quite rare (such as Villager/Wii Fit Trainer/etc). So if you want to get them all, you'll need to spend a lot of money to get the older ones, and make sure to pre-order the new waves before they become scarce. I certainly think they make for a fun hobby trying to collect at the $12.99 MSRP each, but definitely don't think they are really worth $30-60 each that some of them are going for now.
So overall, they definitely make for a fun gameplay extension for the games they are compatible with. But fortunately, they are absolutely *not* required to fully enjoy any game since they play very minor roles in the games. I personally enjoy them more for the collectibility aspect. So I will leave it to you to decide if they are worth buying and how you use them. I am definitely enjoying my amiibo collection so far, and look forward to the ones yet to come. Good luck trying to catch 'em all!
*Summary*
Pros:
[+] High production quality
[+] Fun to collect
[+] Gives you great in-game bonuses/items/perks
[+] Not required to fully enjoy any game
Cons:
[-] Rarity on some amiibo makes it difficult/expensive to collect them all
[-] NFC chip can't be read without removing amiibo from packaging