Oh, you should definitely add a copy of Brainstorm too, for another way to cheat stuff onto the field from your hand and potentially trigger Imoti more.

I don't normally recommend cuts, but I can't imagine the Hydroelectric Specimen  ^Flip is doing much for you, is it? Also, how about Tidal Barracuda instead of Gandalf, Friend of the Shire?

Thanks for calling on me! I'll give you a little pile of recommendations here, take in mind your pod, budget, and playstyle as you consider these.

On finishing out the game at Haste speed, Concordant Crossroads is a reliable way to do that in Green. The downside is you might Cascade into it and give your opponents Haste and make it targetable before you've reached critical mass. Crashing Drawbridge is a more one-sided creature version of this - nice Haste enabler but has some definite downsides, it's very vulnerable to removal being an Artifact Creature, and it has summoning sickness itself.

Brinelin, the Moon Kraken could be useful for removing problematic blockers or combo pieces, to clear the way for you to get more damage in sooner. Repeatible removal like this can also be very demoralizing for opponents.

Also, this deck might have a use for the spell Time Stop, to end a problematic opponent's turn on their upkeep while ramping or generating a body that you can swing with on your next turn. Pretty good deal.

Have you thought about adding Krosan Drover for ramp? It would reduce the value of ~14 cards. There's also Thryx, the Sudden Storm. Might even want to consider Zendikar Resurgent for ramp and card replacement. Thunderous Snapper and Up the Beanstalk also give great card replacement, especially if you Cascade into a MC>4 spell.

Thunderfoot Baloth will allow you to finish out the game faster with its Trample and +2/+2 anthem effects. Craterhoof Behemoth is another example of this. In this deck, Shark Typhoon will generate big evasive bodies that can rack up damage fast.

Once you get some Cascade online, the card Selective Memory could be used to thin your deck of the nonland cards you don't need, so your Cascades are always hitting big stuff (or whatever you need in that game at that moment.)

A huge gas piece you are missing here is Scroll Rack. You can use this card to literally stack your deck with the cards you want to Cascade into, in order. So if you're going to cast an 8-drop from hand, use Scroll Rack to put your 7- and 6-drops down in that order, get two free and predictable casts.

Speaking of explosive Cascades, have you considered Jadzi, Oracle of Arcavios  ^Flip? She and Imoti could have some pretty devastating chains. If you ignore all my other suggestions and add only one card, make it Scroll Rack - if you add a second, make it Jadzi.