Right? Soon enough I’m going to post a Highlander Druid deck list which I believe to be a tier above this. Let me know how well your games/experimenting goes and if you have any recommendations for improvements.

In terms of direct replacements there isn’t much, but I do have a few cards in mind that fit the curve well. I’m a big fan of School Teacher & Multicaster. They have been in previous iterations of the deck and provide plenty of value. Royal Librarian is also somewhat of a replacement—single target silence plus tradable. The main reason I find Sivara valuable is: once you have Tidestone of Golganneth (Queen Azshara relic), you’re able to potentially receive 10 (15) extra spells (+Brann) or inconsistently 25 using Zola, too. It is of course best to do this once you’ve used Reno. Let me know if you find better replacements and I can start recommending them to make a more budget-centric list.

After some testing this checks out. I’m swapping out Mossy Horror and Fireball for Fire Sale and Venomous Scorpid.
As per the points you mentioned, the swap seems obvious here. Adding in another tradable card is pretty big for consistency in the deck. I had actually considered Fire Sale over Mossy Horror when originally putting the deck together, however, having another minion for the opponent to deal with seemed more worth at the time. Yet due to us removing Fireball for another wildcard spell, we can just use that slot as our other body. I appreciate your criticisms of the deck and if you have more let me know.