I can see the "vulture method" working pretty well, but man, it was just soooooo sloooooow and booooooring. Even with modded, fairly-ridiculous stuff, where I could just go stomp things like Godzilla.
That, and the prospect of roaming around like a character in a Dickens novel ("please, sir, just a few XP for my wee sickly brother") scavenging XP just doesn't appeal to me. Worse yet, if you did that, you'd probably want to either stay cloaked or be faster than anything that wanted to eat you, so that you could get away, so no Rez. So, am I playing a pew-pew game or am I Solid Snake?
If I hadn't modded a few things, it would have been even worse than it actually was; at least with the modded stuff, I kept using several of the Missiles all game, because they actually had a point besides being Cloak debuff / Zombie removal.
The biggest beef I had was with beams vs. cannons, though.
That top-end upgrade was a non-choice; Fusion Beams would only make reasonable sense if every single Specialist you slotted gave you beam distance (in theory, that'd give you almost 2X Beam range at the high end). I'd have to check the DPS / power ratios, but probably they're favorable.
Even then, I think Particle Cannon came out on top, because of its base range.
Both do Universal damage (i.e., no specialization or penalties) so the only real win for Fusion Beams would be every-frame damage and no volley effect. Particle Cannons would be better for long-range kiting (even without touching the Specialists modding-wise, I had cannons shooting off-screen pretty fast).