I watched your replay of the top 8 Steve, and I really enjoyed it. It is surprising how many lines there are to discover as you play the deck over time. I found that I had to work through many of the same situations that you faced. Something interesting that I have found about this deck is that most Dredge decks, no matter the build, are very effective at doing certain things. It can be a matter of what your opponent was playing, or what both of your starting hands were that decides which Dredge variant is successful on a given day.
I have found that the more I play the deck in this meta, the more I lean toward a certain strategy. Because there are fewer combo decks like Paradoxical Outcome, and more decks like Mud, Dredge, BUG, and Xerox, I have found that I like Pitch Dredge with Bloodghasts and Prized Amalgams. I also only use one or two Hogaaks and no Dread Returns. This strategy allows me to apply pressure, Cabal Therapy more aggressively, but still have counter spells to stop broken cards.
I have found that side boarding Unmasks to use when you're on the play, coupled with counter magic and removal is very difficult for the opponent to deal with. I will also normally side out Hollow One against decks that use Dack Fayden, but not always. When I face Dreadhoarde Arcanist decks I am more likely to keep some in because their mana base doesn't seem to allow them to cast it as quickly as other Xerox decks. I will also side out Hogaak against combo decks frequently.
Hogaak is an interesting card for this archetype. It provides Dredge with enough muscle to operate without a Bazaar in play, and can be cast through sphere effects. My opinion of this card is that it is better than the Dread Return packages when there is less combo, or a need to end the game quickly, or on the spot. Hogaak also gives the player the ability to brute force damage through against blue decks when they attempt to win the aggro way. This is important because it can be very difficult to resolve a Dread Return against them. If they counter Hogaak is doesn't even matter. It can just be cast again. You can even gain value from bridges by using the legendary rule with multiple Hogaaks.
The Dredge mirror is particularly interesting. My opinion of this matchup is that it is seldom decided by grave hate, but rather from gaining value from Bridge from Below while removing the opponents bridges as fast as possible, going so far as to cast multiple Cabal Therapies to accomplish the task. If one of the players has Elesh Norn, that is probably the best card for the match, but it isn't something that can happen all the time. I have played with Leyline of the Void and Ravenous Traps, but there were so many games where they just went to the graveyard, and could have just been something else. The cards are good, but I think it is more important to focus on the Bridge from Below tactics.
Having shared some of my thoughts on the deck, I will say that I would be comfortable playing at least ten different configurations of the deck. I like Dredge with no counters, super pitch dredge, Bloodghast dredge with Force of Wills (with or without Dread Return), and Mind Break Trap variants. I also like numerous sideboard configurations. I have found this to be a very interesting and fun deck to play, and I hope to keep finding new strategies with it.