I like
As regards the Prime Directive, perhaps say that worlds under a certain economy value are deemed to be pre-warp and thus can't be taken by the Feds?
EDIT: After a bit of mucking about with the map editor.....
General rules
Starting Hex values:
Federation internal Hex: Econ 15, Strength 5.
Federation Border Hex: Econ 15, Strength 10.
Romulan Internal Hex: Econ 10, Strength 15
Romulan Border Hex: Econ 5, Strength 20. (Yes, the Rommies are paranoid)
Klingon Internal Hex: Econ 10, Strength 12
Klingon Border Hex: Econ 10, Strength 15.
Neutral Hex: Econ 5, Strength 5.
Terrain effects:
Black Holes, Nebulae: Economy set to 0, Strength set to 5. Usually neutral, since there's nothing of much value and nobody wants them.
Asteroid belts: Economy-5 on base ownership. (Loss of normal trade, but there's duranium in them thar rocks...)
STARBASES give +5 Economy and +10 Strength to a hex.
COLONY WORLDS give +10 Economy and +10 Strength.
PRE-WARP planets have no effect on their hex.
HOMEWORLDS give +50 Security and +55 Economy. Romulus, Earth, Vulcan and Quo'nos are considered homeworlds.
Miscellaneous effects:
Prime Directive: NEUTRAL planets with an Economy of 5 or less are deemed to be "pre-warp" and are thus protected by the Prime Directive. The Federation (and, by extension, any allies) are not allowed to enter such a hex until another faction takes control of the hex. Once that happens, the planet is fair game for anyone.
SHERMAN'S PLANET: A Colony World just on the Fed side of the Fed/Klink border, Sherman's planet was awarded to the UFP by the Organians after a well-publicised incident involving an (allegedly) rogue Klingon agent, 10,000 metric tons of quadrotiticale and 1,771,651 Tribbles. The Klingons have been trying to get the planet ever since. In game terms, both the UFP and the Klingons can claim a VP bonus for holding the planet.