Something like Perplexicon could definitely provide depth and variety, but several problems arise when handling the more powerful or useful words/concepts. In Cabal (which I just realized I dropped out of without a word of notice, sorry), you balanced it out by making people look for words themselves, which both limited the amount of words one could know in both temporally and numerically AND allowed you, as GM, to choose what words people got/were able to get to a large degree, making it hard and/or unlikely for players to get highly potent sets of words that would steamroll majorities of challenges. If obtaining the words you want was the challenge in this system, then another system might alter getting the STRENGTH of those words/concepts, sorta like what you did with Invokers.
Mages could choose one or two concepts, then get one or two random concepts assigned by the GM. Of course, the choosing part should probably have some description of what concepts would/wouldn't be acceptable. More useful/applicable concepts (such as Flesh, Shielding, Fire, Sword, Time, Lion) would have less potent effects than more specific/niche ones (Pillow, Feather, Smell, Gauntlet, Helium, Tapeworm), whether through roll bonuses/penalties, increased cost, or by limiting how far/much a single spell could do. Pairing versatile, weaker concepts with stronger, limited ones would be effective for multi-concept spells, balancing power and usefulness, incentivizing players to limit their skillsets to having few wide-range concepts while still allowing specialists to exist on this spectrum. Anyway, on an individual scale, players could be able to upgrade their concepts to make them stronger. This might be where the magical resource comes in, both in upgrading the concepts and/or as a "maintenance cost" for having stronger concepts, requiring magical energy (perhaps the magic gasoline) every so often to maintain their ability to use it (whether downgrading it or taking away the ability to use it if one doesn't get enough), proportional to one's magical power.
If the concepts are upgradable, we should consider some branching form of upgrades. I can see _ ways to upgrade it: Reduced mana (or equivalent) cost; Increased maximum scale (affecting larger area or having otherwise bigger effect); And conceptual range (allowing the applicable effects of the concept to expand. As example, "Flesh" could push/pull it at range at low levels, proceeding to summoning lumps of flesh, repairing it, growing it, and then mutating it). Alternatively, you could just go Upgrade=Higher Roll Modifier and Added Aspects of Spell(larger, stronger, more potent, higher degree of control, etc.)=Decreased Roll Modifier.
On a separate note, I like the "Wizard Gang Wars" style you described. If you do do this, I would suggest considering some wide-scale enemy that all PC gangs would be opposed to, providing a reason for cooperation at times.
Also, I'm expecting a ninja assault of some sort. Wish me luck.
Yup, three of 'em. Harry, the inter-gang politics you mentioned seem rather interesting, allowing for traitors, double-traitors, mercenaries, and circular hierarchies. NAV, that would pretty much fall under the Wacky Races RTDs, but some degree of creatable vehicles and other large-scale weapons/utilities could be interesting in the second proposition.