Welllllll... to be honest, unless it's a sure thing then strategically it doesn't make much difference. Which from your description, seems to be the case. If they 'tend to' use bordering AI world warp gates, that's not the same as always doing so. If I gate raid all around a planet, then I know that planet is pretty safe. Sure, I'll have to watch for bordering worlds beefing up reinforcements and stalking through, but I can always sweep a fleet through or send in a suicide squad of disposable units like shredders to clean that up. An Exo-wave isn't the sort of thing you can toss up a couple just-in-case turrets to deal with though. Even if there's only a 5% chance that they will come from a direction that I've gate raided, in a scenario where they do, and where I haven't set up exo-wave capable defenses, they're probably going to roll right through and kill my homeworld. The type of defenses you need to handle those waves aren't the sort you can set up in a frenzy after they've just spawned and are 10 seconds from warping in to your world. Those spirecraft are vicious!