I'd say it depends on a situation. For some situations it would work (when you are really doing something to get prepared), for others it wouldn't.
Just imagine: "Завтра я собираюсь встретиться с друзьями" - in this context, it just expresses your intention or plan, but does not imply any "activity", you are not doing anything to prepare for the meeting. Similar example: "Вечером мы собираемся вместе посмотреть фильм" - there's no shade of "preparing".

But sometimes, yes, it's more like "preparing".