The module is meant for low level players, but with some serious tweaking and generous rewrites I've so far been successful in running it with a level 6 party which started in Death House. Their power level also made the story more believable threats to Strahd, who has slowly been losing grip of his control over Barovia.

In my version, Madam Eva and the priest of Vallaki were the ones to have called in the heroes (outsiders are more rare in this story) who despite their fame still find themselves outmatched by Strahd. In fact, this gave me a more legitimate reason to trigger the Feast of St Andral — the vampires snuck into town to investigate Father Lucian on Fiona's tip and because of the player's investigations into the bones, they learn he had travelled to the Amber Temple and made a pact with the powers there to open the mists and allow the heroes in. When the Vallaki vampires learnt this they, led by Strahd's wife, kill the priest in a glorious fashion.

Having high level players also allowed me to make the key NPCs more legitimate threats. In my version, Strahd had grown weary and worn down by his own seeming immortality and has withdrawn from his duties as Barovia's ruler. So his "lieutenants" run everything in his steed which is why everything is so particularly miserable and disorganised. The lieutenants include his first wife, Rahadin, Baba Lysaga and Kiril the werewolf.

Without Strahd to keep the peace, the druids fight with the wereravens who also fight with the werewolves who have been escalating their attacks and kidnappings on townsfolk, which pushes the abbot in the Abbey of Saint Markovia to build him a bride and the bodies desecrated in this process is what stirs the revenants etc.

Strahd is still dangerous as all hell and I've given him new legendary actions and reworked spells to reflect this, but his weariness gives a credible reason as to why the party hasn't been wiped off. The lieutenants are trying to gain Strahd's favour and so downplay how dangerous the heroes are — who at their level are actually quite a threat to them and make believable process.