I saw [[Topiary Lecturer]] during prerelease and had to do a double-take. 3 mana for a mana dork is definitely a hard sell, but it being able to very easily tap for 3+ mana is a huge positive. With the few games I've played with this card in my pod, it almost immediately required an answer or it just runs away with the game with the mana advantage it provides.
I think what makes it so good is that you can fairly easily increment before using the mana the turn it loses summoning sickness. After casting a 2-3 mana spell, you still have 3 mana to use on other spells, which is huge for decks that are looking to curve out on T4 while also holding up interaction. I see this 3-drop as a mana dork that taps for 2 since you only need to cast a spell that is 2+ cmc to trigger the increment.
It also has the added bonus of just continuing to increase over the course of the game, which basically requires interaction before it gets out of hand. I was able to fairly easily tap for 5-6 mana with this thing on the following turns, and that is something no other mana dork can really do without additional support. I'm not even mad if someone blows it up since I know that I have bigger threats in green.
Am I crazy for thinking this will be a staple in green decks for casual EDH? It reminds me of [[Icetill explorer]] in which both abilities work so well together that it becomes a value engine on it's own.
Edit: Lots of comments comparing this to cards like [[Kami of whispered hopes]] and [[Gyre sage]]. Although yes I agree these cards are good, being able to have an engine that powers itself is a huge positive to a card. You get more mana for just playing spells, which is something you are already wanting to do.