If 18 dice is simply too inaccurate for you because it could potentially be dodged then I presume all the street sammis in your game walk around with a grenade launcher and nothing else? No point in a pistol or a good combat shotgun? Which is what you are telling me to use, despite they can be dodged too and i would probably have a lower pool with it.
Nah if I wanted to have a gun, I would make a gun build work. I don't like guns that bite me with no real benefit over and above a gun. I don't see single-directs as worth it, basically ever. Combat is not remotely the best school of magic this edition (a marked change from 4e). Lightning Bolt is a waste against mooks and a risk of outing yourself as the mage with no benefit against anything that actually matters.
This trick works on special targets fine, but do you really want to drop 200 nuyen on every attack you make? That adds up fast and really cuts into the profit. Direct spells are good for targets too tough or too dodgy to otherwise hurt, but for smacking a run of the mill ganger or mall cop I think you would be further ahead with Clout.
If I am really worried about reagent costs, then my GM is a stingy bastard with run payout. Because if I really need to worry about reagent costs, then everyone else is really worried about ammo, and, meh, that kind of gutter-poorness over combat resources is not what I come to Shadowrun for.
Besides, I rarely throw combat spells. This edition majorly incentivizes sustained area debuffs.