In space PvE, Acc is. . .less important. Defense values of NPCs are pretty low, so they're easy to hit. Best mods to use are Dmg, CritH/D.
In Space PvP (where your stats are actually put to the test), Acc is crucial. You can't DPS if 2/3 of your shots miss the target due to high defense values (which happens a lot with escorts, especially if they're running Omega or evasive maneuvers). So, you can go with a [Acc]x2 [CrtH/D] setup, or run [Acc]x3 (which is expensive, EC-wise).
ACC is still a good choice even in PvE... excess vs low Defense vessels goes towards increasing Crit H chane... which means double damage... more thas a [DAM]x3, but certainly less frequent.
Then again, you get versatility to be well-equipped for PvP as well if you favor [ACC].
And yes, [Acc]x3 is EXPENSIVE... but worth the grind.
if you must have fleet advanced space weapons..which are good for PVE, but generally suck in PVP, get the [ACC] modifier...why? that ACC in PVE is actually critH and critD.
i run pure [borg] MK XII for space stfs, and elite fleet for ground everything (including stfs) since the borg mod on ground is not so fantastic (each shot +15) 2 dmg modifiers are equivalent to that. meaning that elite fleet ground weapons are nearly the same for borg as the actual borg weapons.
for anything else in space i use ACCx2 with critH/critd and for my turrets i use advanced fleet weapons ACC
also my torpedo tube is advanced fleet, but only because i had no chance to get my hands on a quantum launcher with atleast accx2