I've started playing ME3, and was wondering if there's now any point in downloading LOTSB? I'm not too far in to ME3, I've just recruited Garrus. Will LOTSB have any bearing on my game if I play it now?
No, it will not, from a gameplay perspective. But imo it's good for you lore-wise. Things about Liara will change, which will be explained in the Lair Of The Shadow Broker DLC, and those changes will be in effect in ME3 weither you play the DLC or not, so it might be wise to do it.