I actually lost interest in them quite heavily these past few months, for no clear reason (except possibly Nintendo's current over-reliance on and initial understocking of them).
I did go though a period in which I made a habit out of checking any store I came across for them wherever I went (including Germany - where they had quite many available compared to the UK - and Japan), but not anymore. I might buy some of the DLC Smash characters still, like Ryu and Cloud, simply because I like having some physical version of those characters (without having to buy other toys), but I probably won't start collecting any new series after Smash (so no Animal Crossing etc.).
For the Smash series I limited myself to the individual characters I really liked instead of trying to collect them all. Being a bit OCD with regards to collecting, for the most part I avoided buying characters that come with their own series' subsets since I'd likely be itching to collect those as well. This meant avoiding any Zelda or Fire Emblem characters for example (though I made an exception for a few separate Mario ones).
I got the following 6: Dr. Mario, Wario (my favorite), Bowser Jr. (mostly because I like the Clown Car), Mega Man (my first), Olimar, Little Mac (only because I came upon him randomly for a normal price). I had my eye on Pit and Fox as well, but decided not to get them as this would mean collecting the others in their subsets as well (i.e. Falco, Dark Pit and Palutena). Duck Hunt Dog and Mr. Game & Watch seem cool as well but the former comes from a game I never really cared for that much while the latter needs to be bought 3 times if one wants to have enough stands to display all three of his versions (OCD, remember?)
Oh, I did get the three Splatoon amiibo's as well, mostly to show my support for this new Nintendo IP beyond buying the game itself.