A deceptively powerful improvement over the basic Emergency Cache. Even leaving aside the powerful Strange Solution combo, this upgrade is fully TWICE as efficient as its base, if we assume that one card is roughly as valuable as one resource:
Standard gain resource action: 1 action => 1 resource: baseline efficiency.
Basic Emergency Cache: 1 action + 1 card => 3 resources: 1 point of efficiency (2 additional resources - 1 card).
2XP Emergency Cache: 1 action + 1 card => 3 resources + 1 card: 2 points of efficiency (2 additional resources - 0 cards).
3XP Emergency Cache: 1 action + 1 card => 4 resources: 2 points of efficiency (3 additional resources - 1 card).
This puts Emergency Cache on similar footing as Cryptic Research (which is a straight-up net of two cards with no action cost), with the added benefit that it's impossible to backfire by drawing weaknesses.
The real question is, can we justify spending an additional XP over the 2XP Emergency Cache? Yes, I think we can. The ability to convert one card into four resources is more tightly focused than the ability to convert one card into three resources and a card. Being able to pull out a Lightning Gun or a Leo De Luca quickly can make a huge difference to an investigator's chances.
Obviously, Hot Streak is on a whole other level, but any investigator without access to higher-level Rogue cards should consider picking this up.