Just thought I'd mention the self destruct isn't a completely useless extra. Though blowing up your droid may seem like a bad idea, it is worth noting you don't lose studs (from the act of self-destruct). This means that you could blow up to prevent losing studs from falling, or you can send your droid, which is usually ignored by enemies, into the middle of a bunch of them, and boom. If you opt for the invulnerability extra, it's kinda pointless entirely, but it's an option open to other players.