One of the things I am hoping to avoid with my layout is getting into model airplanes the way I backed into collecting 1:43 and 1:48 model cars and trucks - it started as something to get for the layout and quickly took on an addictive life of its own. Luckily, the only aircraft I have so far are two: a Lionel blimp piggy bang that I keep in my study as a curiosity, and a big model dirigible (about a meter long) that I can hang over the layout.
Model planes would obviously be addictive if you got too close . . .