IMO, the way controlling magic nodes impacts tactical spells is both overpowered, simplistic, and ignoring so much that could tie in to the gameplay.
Rather than have nodes give a flat out doubling or 100% bonus or whatever it is now, how about instead having node control give a smaller, more sane bonus that is impacted by your research, buildings, sov's items, or even sov abilities (that don't exist right now). So maybe the bonus gets more extreme as you invest more heavily.
For example, maybe nodes give a flat 25% bonus to tactical spell effectiveness (seems to only apply to dmg but could apply to duration on buffs/debuffs or whatever else too).
The game has a bazillion technologies to be researched - why not make certain magic techs (in the SHARD line perhaps) increase the effectiveness of your shard control bonus? Or unlock buildings that you must build (shrines/temples/labs/anything) that bump up shard effectiveness? There seems to be a bazillion buildings too, what's a few more? 
There could be whole lines of items in the game - rings that give 5% bonus to fire shards and whatnot. Or that just give a 5% generic shard control bonus. Whatever. It adds more variety and decision making to item use.
Lastly, there could be a sovereign profession/talent/whatever they're called that gives a 5-25% bonus to shard control effects. Variety is good. The game is about magic - a sovereign ability that ties in to shard control seems to be a fabulous idea. /pats self on back
I like for their to be options and making critical decisions is what makes these games compelling. If you break it down rather than just giving a huge bonus, the player has more decisions to make. For ex, if ALL of the above was incorporated, a player could really invest heavily in making their sovereign a magic user of note, instead of - haha we got a node or 3 and now we pwnzerize the universe by default!