You are forgetting one major issue here: its passive. The active on Frostqueen is nice, but its spellthief's passive that makes it a good item. First off, passive gold is always good on a support. Its especially useful for supports that need expensive AP items such as Morg. Then, you've got the other half that really makes it an early game nightmare. Dealing damage to an enemy with a spell does an extra 10 damage and grants you 5 gold, up to 3 times per 30 seconds.
Looking at that mathematical, if you use it to its fullest capabilities, youre getting an extra 15 gold every 30 seconds. Thats the equivalent of 0.5 gold per second or 2.5 gold per 5 seconds. thats superb. Add that to its original 2 gold per 5 and you have a godlike amount of old income, not to mention mana regen AND extra damage. Upgrading it to Frostfang gives you 5 more gold and 5 more damage and more mana regen. That means at its most effective you are getting an extra 7 gold per 5 seconds. That is insane. Now, you won't be operating at full capacity most of the time, but even at half that the extra 3.5 gold per second is still one of the best in the game.
But why does it work on support morg? Her soil. You should be upgrading her soil last as support morg because of how hard it pushes and how poor its scaling is. Its great in midlane, but it does everything you don't want as a support. It pushes lane too hard, it steals minions on accident, and does very little damage if they aren't standing in it for 4/5 seconds. Buying Frostfang turns it from your least useful to most useful skill as support morg. It is incredibly easy to proc all 3 stacks of Frostfang with one soil on one target. This means every time you cast it youre going to get an extra 15-30 gold and do an aditional 30-45 damage. That means if they stand in your level one soil for just 2 seconds, youre doing to do 72 minimum damage, PLUS the adition of their missing health. This is an extreme zoning tool for morg, and the best part is you only need one point in it early on. That equates to no extra mana cost, no unintentional pushing of wave, and no accidental cs stealing.
You need this item as support morg, end of story. And you should upgrade it AT LEAST to Frostfang to get the extra gold and damage. It may delay your Hourglass, but probably no longer than laning phase. Remember that most of the time youre going to get between 400-800 gold from this item JUST from laning phase. Late game it can be sold for Chalice and whichever upgrade you choose. Either way, It is far more valuable than the extra 5 minutes it will take to get your hourglass.