I haven't bought any so I'm no good to you. I can give you some reasons I don't buy them, if you want.
Their implementation does bother me to varying degrees. If the content unlocked by amiibo is only meant as a reward for having already bought it rather than an incentive to buy one, why not offer that content digitally at a lower price? For example, the Link amiibo costs $13 and gets you an exclusive function in both versions of Smash 4, a Mii costume in Mario Kart 8, a new weapon in Hyrule Warriors, a costume in a One Piece game, a plane design in Ace Combat, and probably another small thing here and there I'm forgetting. Why not let players buy the HW weapon for like $3-4 and Mario Kart, One Piece, Ace Combat costumes for $1 apiece or something, and keep the Smash functionality exclusive (as well as little bonuses like getting rupees for scanning amiibo in HW)? That way owners of the amiibo get the 'bonus' -- they have exclusive functionality, and don't have to pay for DLC related to that character -- while non-owners aren't looking at minuscule but non-negligible amounts of content locked behind a baffling $13 paywall.
Oh, a $13 paywall with very limited availability in most cases. This is not a separate issue from the price. I think it's very clear by now that the amiibo shortage is entirely deliberate on Nintendo's part. If they overship a character, they risk seeing its price reduced, and I think the depreciation of amiibo values is the number one thing they're trying to avoid. Those little bastards are going to cost $13 forever. You'll never see them on sale. You'll never see them in bargain bins. Nintendo is going to keep stock on a very, very tight leash to ensure exactly that.
Either of these issues wouldn't be too much of a bother on its own, but the two are an ugly combination. Simply fixing the shortage situation wouldn't even solve the problem. As long as content is tied to amiibo, unless every single amiibo is available at all times you wind up with limited edition content in games. Link is pretty common, but think of the Fire Emblem characters in Codename: STEAM. What happens a year from now when these characters can only be bought second-hand at a huge markup? What about five years from now when they're damn near impossible to find? That content is lost forever to new players. I suppose you can edit the data on a Mario amiibo to make it identify as a different character, but that solution isn't exactly endorsed by Nintendo, and might be more trouble than it's worth. At the very least, I doubt any good samaritans would be willing to spend $13 on a Mario amiibo, edit its data, and resell it for the same $13 price, which means you'd be looking at some kind of markup anyway.
