I think that the key word here is 'eventually'. We can absolutely keep tapping Princess Fallenstar for Lizardman relics in the hopes of getting weapons and armour, and getting our hands on some Lizardman military equipment from there is likely if we have an unlimited amount of time, but keep in mind that those relics are being recovered from a buried Temple-City. That makes it good as a source of representations of 'generic loot'; for armaments specifically, though, we'd be relying on a miner breaking into a weapon-crafter's workshop or armoury (and then managing to smuggle some of the contents out, which might be tricky for objects that large, unwieldy and distinctive). Sure, it's going to happen at some point, but we don't know how long we'll have to wait until we get the right booster pack and in the meantime Luthor Harkon will be tapping his foot in the background waiting for an exhibit that we could have already assembled. By contrast, I'd say that personal acquisition is fairly reliable in the case of military equipment; there's bound to be plenty of it kept as trophies in Awakening itself and, if that's somehow not enough, there'll be people there who know of old battle sites where such items can be recovered (albeit with greater difficulty).
(If that convinces you, I would note that Plan MMM only has that as the one personal acquisition option and leans on the Princess for the other two, so it should be more reliable than most of the popular plans in that regard; would be delighted to welcome you aboard if you'd be amenable!)
I do like MMM's double Princess acquisition, but weapons and armor seem like a bad use of the personal acquisition. Just about anything we get from a Relic pull ought to be useful for some kind of exhibit, so I don't see a good reason to go that route as opposed to going for bulk.
On the other hand, the castle option in the first and second leading plans strikes me as an
unusually good use of a personal acquisition; I'm just less impressed by the way both of those plans do personal acquisitions twice. If there was a compromise plan that did double contact acquisition and also grabbed the castle, or maybe swapped in Investigate for one of those actions, I'd be all for it. Something like:
[X] Plan: Optimized Castle Prep
-[X] Acquire Relics via Princess Aelsabrim Fallenstar (x2)
--[X] Skeletons
--[X] Relics
-[X] Acquire Relic (Castle - Fire Serpent Island)
or
[X] Plan: Optimized Harkonnian Institute
-[X] Acquire Relic (Castle - Fire Serpent Island)
-[X] Acquire Relics via Princess Aelsabrim Fallenstar
--[X] Relics
-[X] Investigate (Luthor Harkon's many adventures)
EDIT: Also, adding this one in as an approval vote, despite the way it includes two personal acquisitions, simply because it hits the mark a lot better than the other plans seem to.
[X] Plan: Pirate Flags and Castle
-[X] Acquire Relic (Castle - Fire Serpent Island)
-[X] Acquire Relic (Pirate Flags of the Vampire Coast)
-[X] Skeleton (rare)