I could be rather mistaken in this, but i haven't found a place that's better to grind in terms of pure exp earned than Cerulean Cave, which is sadly lacking, so my plan to light up on the fast track is to set up rematches with all the gym leaders, through severe date/time abuse on my DS. I've isolated the gym leaders that would be easiest to beat for each of my 7 pokemon (the six listed in the sig, plus Palkia who i'll be using in lieu of Quagsire for the Elite 4, but Quagsire needs to train for Red further down the line), and i'll just mechanize the process until i get everyone up to 70, Abomasnow up to 73, and Palkia up to 75, to appropriately tackle Lance.

Is this the only way for me to get up to fight Elite 4-2, or is there something less complicated than this where i can get similar levels of EXP (say an area where the Pokemon are in the mid 40s or 50s or so)?

Well, your strategy does seem solid, although I my training for them stopped when Dragonite reached level 68, which was more than enough to survive Salamence's Dragon Claw (if he didn't Crit) and outpace all the rest of his Dragon pokemon. With Ice Beam, Dragonite took care of them all.

Gyarados was no match for my level 64 Electivire, and then Charizard was also taken down by a Charizard level 64, with Rock Slide.

I used the Elite 4-2 themselves as training regiments for my pokemon. I always went as far as I could go without using items and then just repeated. Exp. Share is also a good thing to use.