That crystal would also do a number on my head if I ticked the wielder off when he was low on mana.

It could also aid endurance, for those long travels (using it as a walking-stick).
A big crystal would make the sticky heavier and slower to swing, but that is irrelevant to the magic. A staff is not a wand. You channel the magic through it to amplify or focus it, not wave it to shoot it out.
How it could help mana is if you could store the mana in a crystal/orb, like an extra battery. While it's charged, you could use it as a lens to focus magic, and it could have all kinds of crazy effects. If you start running low, you could opt to drain the crystal and have more mana, but then the fancy effects would be lost until you recharge it.
Before one of the glyph-crazed monkeys objects, the big crystal providing us light is not a glyph. So the possibility for magic to be stored or modified without glyphs does exist. Besides, Laanx wants mastery over the crystal and it's power, ignoring Talad and his glyphs. So I'd say these are possible. Maybe you couldn't cast a spell with just a staff, but it could certainly enhance it or do other things.
It could be made from a stick that had one of those "natural" glyphs forum upon/within it, and maybe a fallen piece of the crystal attached. Or it could just be "enhanced" by a spell from a more powerful mage. Yes, that means it could slowly drain over time. Don't swords already do that though? Same idea. To repair it though, you'd have to cast a powerful and lengthy spell, that would completely drain you for several hours or days. Cool things come at a cost.