In the eyes of the Party, Winston poses a true threat. The Party maintains power by using mind control, by teaching others to think in ways that benefit the Party (Big Brother). It seems reasonable to assume that the only real fear of the party is losing its power; its power can only be lost via the power of free thought. Freedom is contagious; its power grows many fold with the addition of each person who recognizes some evil in Big Brother. If you think of free thought as a contaminant (from the Party's viewpoint), it may be easier to recognize that Winston, as person aware of truth, could share that awareness with others. Each person who realizes some degree of truth may infect myriad others with his knowledge. In essence, the Party must stop Winston, and others like him, or risk everything they have.
I don't really think that the Party has gone to any extra lengths to ensnare Winston as we saw when he was arrested. Winston saw the most loyal Party member he knew of, Parsons, right there with him in the cell. The Party puts effort in any and all insurgents or even people who pose a slight possiblethreat to the Party. Parsons was "outed" by his daughter and had to endure at least a brutal interrogation. People who prove to be more of a threat have to visit room 101 if they aren't respondent to the brainwash attempts, but Winston is treated no differently than any other person who goes against the Party. It seems that they go to great lengths to us because we are reading Winston's story, but Julia was subject to the same torture as she mentioned in their final meeting. While the Party did lay quite an elaborate trap for Winston, it can't be said with any certainty that the Party doesn't devote time doing the same to others just like him.