No, the sponsons are additional.
And it's always worth adding the Door Gunners on Vendetta's, unless you need to find 10pts elsewhere.
The reason for this is that they have to move at combat speed to fire all 3 Lascannons. As moving at combat speed allows them to fire their Heavy Bolters as well, they are a useful addition, as you will almost definately rack up the 2-3 kills needed to offset their heavy bolters cost.
In addition, it makes it "not a waste" against Hordes, as 36 shots of heavy bolters in a game is decent enough, but not dangerous to warrant targetting as it is reasonably tough.
As a general rule, Vendetta's - YES, Valkyries - NO.
The executioner - although 5 Plasma Shots sounds nice, it's way too expensive. If it's a major threat to an opponent (Marines, namely), then it will be a primary target. And such targets have ways and means of taking it out - Drop Pod Melta Dread, Stormraven, Outflanking Melta Bikers/Melta Chosen, Land Raider Assault Terminators. If it's not that much of a threat (Orks, Tau, etc), then it is either easy Kill Points, or easily tied up. The extra armour is not that good for its expense compared to Lumbering already providing its benefits half the time. Personally, I'd drop the side sponsons, and run it just as a Tough to crack Plasma Cannon, and ram it down the enemies throat, targetting blobs of enemies and blocking LoS.
Drop the Extra Armour on the LRBT, and just use it much the same way - run it down the enemies throat, and force it to be dealt with. Armour 12 is reasonably tough to crack. When static.
The Twin Basilisks, not a fan. They have to be in LoS so as not to have 3/4 of the battlefields width ignored, and are far too delicate - the main gun and side armour 10 is far too poor to encourage that plan of action.
Instead, depending on your opponent, I find the Colossus to be much more of threat, especially in Marine Heavy Opponents. The S6 AP3, ignore Cover makes hiding in cover less of an option. Killing Marines on 2's with no save unless invulnerable after having their transport peeled open by Lascannon/Melta, and finished off by Plasma wielding Stormtroopers is a nice combo. Of course, it's less effective against Green Tide/Termagant Spam, but hey ho.
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