Matt,
Cool that you're testing the deck. It's one of my favorites that I've built. It's not often that a really good Grass card comes out. I disagree with your choice to remove Buffer Piece from the deck. It's a cornerstone to the deck's longevity. Quagsire too is needed for it to realize its true potential. I've tried Swalot and Venomoth and did not like either one. Strength Charm really is not needed IMO because the odds are that you will usually hit a Poison flip over two turns to OHKO any Pokemon with 130 HP. I can see where it would be useful, if you were to go for the Sleep instead of Poison and drop a Charm to keep a Gallade possibly trapped active. But I can't see using Strength Charm at the expense of Buffer Piece. Cards like Venomoth, Swalot, and Sunflora are all great cards to use, but they really do not _maximize_ the potential of Venusaur. Of the three listed, I would say Swalot is the best simply because of its synergy with Venusaur and its ability to be so irritatingly annoying on its own (Gulpin has Amnesia). Swalot helps out in the Blissey matchup tremendously if you are worried about that. DRE for auto Confusion and Poison = niceness and it's second turn.
I would have to see your list and see how much it deviates from mine. For Blissey, you just have to play it safe. Exploit Buffer Piece, and if you are able to hit a couple Giant Bloom flips, you can outlast Blissey. And as I said earlier if you can hit one of two heads on Poison you 2HKO Blissey. It's rougher against Gallade - Sonic Blade is the problem, Psychic Cut is grows weaker as the game goes on. You have to hit a Giant Bloom flip after a Sonic Blade. And you also have to keep attacking with your damaged Venusaurs, so they don't get finished off on the Bench by Gardevoir Lv X. You can beat Gardevoir even without your Powers. Fire is a serious problem, which is another reason why Quagsire helps out a little bit more than the other Grass supporters. And you are right, this deck laughs at damage spreading decks, which is another huge advantage. Celebi is the best thing Grass decks have going right now. It can set you up so very quickly. If you are afraid of using it earlier for fear of KO, you can exploit Buffer Piece on it too, while you power up. Venusaur + Buffer Piece + Quagsire d = a long lasting Pokemon that can deal some serious damage. With a little luck, you can keep that same Venusaur there for at 2-3 prizes easy.
Watch out though, you might get called for necromancy (re: this topic) ;P
~Jim