For manabolts in particular, there's no real difference in going Force 1 and Force 5 (they both inflict 2 drain). Granted, you can go higher than that with reagents, but then you have to actually spend those reagents - and setting them to, say, 8 "just in case" gets expensive quick. After all, it's wasted unless you actually roll those successes, and it takes a while to get enough dice to reliably do that. What's more, once you do, you probably have enough drain to sort-of-safely cast at, say, Force 7 as well.
It's a bigger deal for area spells, though. But still, you're basically expending a grenade's worth of resources every time to probably do less damage than a grenade would. So I don't think it's a massive issue.