1) Corp dev can also do strategic investment; you probably don't want this at an early stage but can be worth considering at a later stage.
2) Corp dev teams don't magically know that they want to acquire you, assuming they're not connecting to you via an existing investor (in which case they probably have some inside knowledge on you already), they may well just be at the stage of trying to figure out what you actually do and how you fit into the ecosystem. So it might be worth having a conversation but not necessarily giving away any secrets,
3) Acquisitions are like investments, having a warm relationship helps. But they can be time-sinks and you have to judge how much time you want to invest when you're not actively seeking.