[JimMorrison]

There are indeed lots of things you can do without expending gems.

However, many of those things culminate in a battlefield wide version that requires gems, and saves you an incredible amount of casting time and Fatigue. Low path mages can put out an incredible amount of evocations, if you rely on only a couple high path mages to do battlefield buffs.

Also, for example, Light of the Northern Star buffs all Astral by +1, enabling your Astral spammers to access higher spells, or to cast for longer, or to get penetration bonus.

I think the key to remember is to keep it simple at first. Have a scout carry some extra gems, or just place extras on a commander/mage that lacks the path to use them. The management of this adds a little difficulty, but it's not that much work to get a couple of large effects added to an important army, and the investment can pay for itself hugely (especially if you use a lot of summons, why would you not want them all Regenerating, or....?).