I should note that I am really grateful for all your help pops, so I don't want this post to come across as ungrateful of your advice:
It complements Minion to be sure, but not that much, it essentially adds one more Minion for 4$. And really after you buy more than one you get diminishing returns out of it.True, you can scatter more Summons in there, but some of the time you just Summon a Summon, which means in the end all you do is eventually tutor one Minion. And now you paid 8$ to get to it (or maybe 12$ who knows). And because you discard to fire each Summon, you are now possibly in danger of killing your Minion engine entirely.
So the most cost-effective way is just to buy one...well congrats you added one more Minion for 4$ and you probably bought it on a turn you didn't have 5$, and early on it let you play one Minion you didn't normally run into...and as we all know Minion engines aren't that strong in the early going. It might allow you to add one more Minion when Minion is piled, but okay, you spend a late-buy to acquire just that. And really Minion is one of the best examples for Summon. It does work really well with it.
Again, I feel really strongly that making it terminal destroys it's usage. It would be often dead on the board. It has marginal utility, because you have to get the actions on the stack and then what you wind up drawing is probably something that just puts actions on the stack (sometimes not of course, but once you add more than action card to summon, you create a randomization scenario that isn't that strong). Making it terminal, kills a fun card, just kills it. It doesn't work that well with engines, even rink discovered this is so. It works, but not as effectively as really just acquiring more of the engine itself. It's real elegance and utility is to summon one powerful card for you.
Actually it's a superb BM-enabler, more than an engine-enabler. Because in a BM+Smithy set up, it can ensure the Smithy fires very often (especially early which is when BM likes to dominate anyway). It tested well when put to this task. One Embassy+one Summon would do well to support Big Money, but I am not sure it would be broken, just effective.
So far, I've seen that Summon is not that great a card to fuel a good engine, because you'd probably rather have the engine card itself. Because usually the cards of the engine itself are better than just tutoring for one piece of the engine. You see your engine card is going to probably keep some of those cards your Summon is going to discard just getting to your engine. (Early in the game for example, that gold can go bye-bye into the discard pile and you won't see it for a few turns, you would have seen it however if you'd just stuck to your engine).
The only real argument I can see against it, is I should govern it somehow so it can't tutor a card that costs more than 5$. That is something I'm willing to concede, but I think making it terminal is no fun at all. The other strong criticism I need to accept is that the "summon treasure" portion is an atrophied limb. It's almost NEVER used, and therefore not really necessary. It helps you only when you do follow the Summon+1 attack tactic, because I guess you can handle the collision of the two by simply tutoring a treasure card. It's like a weak consolation prize when that happens. I could lose that portion of it and not shed a tear.
I think I can make it work as a non-terminal card though and I'll use this next wave of testing to see if I am right.