I feel like the easiest and most obvious answer is to simply scale the mana production up (I also really like Pheryll’s idea of increasing the broken shard cap!). The main problem is that as the scout times increase along with number of provinces completed, which is the number it uses to compute production, it never actually improves very much in terms of mana/hour, and even if one scouts continuously the output isn’t much better than the culture menu mana producers available in each chapter. If this number were balanced more carefully to match at least the roughly the output of whatever the lower-to-mid level event buildings for a chapter give in mana/hour, it would be much more useful; then assuming scouting is taking place close to constantly, it would at least be a better option than the basic culture buildings available to everyone, and if someone cared to use time boosters on their scouts, even occasionally, it could be a very good producer when needed.
I've had it in my city for a number of months now and it is quite nice to get that boost of mana when I scout. (I am, however, about to get rid of it now that my LoGN is boosting my mana production quite nicely.) Technically, it can be used as mana on demand the same as the Dragon Abbey, you would just burn time boosters instead of spells which is probably why the devs have never felt the need to seriously look at rebalancing it.