The primary purpose for separating the saucer from the drive section is to increase the abilities of the drive section in combat. Less mass, smaller size, smaller target, smaller deflector shield, smaller warp field. Power not needed to enclose the saucer in a warp field and a deflector shield are diverted to weapons.
Mass in space is a non-issue.
Trek technology also completely negates mass oriented issues by using subspace fields, that's why in early TNG large ships were portrayed as being able to turn like small fighter crafts.
As for 'enhancing' ships combat abilities while separated... doesn't make sense really because the saucer has power sources of its own to make it completely self-sufficient under sub-light conditions (for achieving Warp speed though, it needs the star-drive) and not to siphon any power during combat conditions while connected to the star-drive section (besides, most combat situations saw the Enterprise-D and other Galaxy class ships connected - even during major battles such as with the Dominion - so the 'enhancing of ships combat abilities' kinda goes down the drain.
Besides, all occasions where we witnessed the Enterprise-D separating (which were a hand-full) was mainly to protect the civilians and non-critical personnel (or in other words, evacuation).
As I pointed out earlier, the Enteprise's strips are over twice as wide (or tall) as the Voyager's. It's not just the case of her having more length. There's more emitter surface.
0 on-screen evidence supports the claim that the length or emitter surface area has any bearing on the phaser power output.
If it did, and if the Galaxy's star-drive really 'shines' in combat while separated... why lose the 'more powerful' phasers ability (especially when basically the only time we saw both sections in battle was versus the Borg, and that was only when the saucer served as a DISTRACTION - usually though, the Saucer was NOT part of other combat scenarios).
You brought this up before and I'm not sure what it has to do with combat ability.
And where do you get the idea that the Voyager has "less amenities?" If the Voyager has two holodecks for 150 people, and the Enterprise has thirteen or fourteen for 1000 people, it's the same ratio of holodecks to people isn't it?
Voyager has much fewer amenities compared to the Galaxy class due to its size and crew compliment, but also to probably increase its combat ability so it can be a match to larger vessels.
The Galaxy class also has numerous recreational areas (amenities if you will) that basically make it a small mobile city of sorts - the Intrepids don't have such 'luxuries'.
As I said, if the Defiant was able to match larger vessels in combat ability, there is no reason Voyager wouldn't be able to do the same (only its size gives it the option to have bare minimum amenities for the crew, whereas the Defiant cannot even have 1 holodeck because its extremely compact).
Facing possible combat with known terrorists, the Voyager would have been carrying a full weapons load, including two tri-cobalt warheads.
Actually, given that Voyager was launched for a 2 week mission to find a LONE Maqui ship (and technologically inferior on so many levels) in the Badlands wouldn't necessitate a full torpedo compliment.
Its entirely possible this was supposed to be Voyager's 'shakedown' cruise - and it might have been a way for SF to test the tri-cobalt warheads as well.
We don't know the full reason, but I find it difficult to imagine that a ship of Voyager's size would only carry 36 photon torpedoes (which were Type 6 and supposedly 'newest' at the time, so its possible SF didn't have more to spare when they launched Voyager and figured 36 would be enough for a 2 week mission).
SF ships WERE launched half-ready before, and Voyager didn't have any additional supplies on board compared to say if they were launched for a deep-space mission (like the Enterprise-D was).