1. The previous clip with Groucho and Chico in A Night At The Opera (1935) was more of a routine using double entendres, puns, misinformation, and exaggeration, not to mention absurdity that made this deal about an opera singer in the contract more lie a business arrangement, than this clip in which Abbott plays the skeptic and Costello the childlike believer who believes that Dracula did open his coffin, similar to a parent who believes that their child lis lying about something that they made up, but the child would say that it's true.
2. Yes. I find that contemporary comedy today does lack the taste, perfect timing and polish of classic comedy routines that modern day comedians omit from their material for a larger audience to a new basis.
3. Their biggest contribution is the classic verbal comic routines that were non-offensive, clean, and family-friendly humor that some comedians today would try to incorporate in their comic routines, they also came up with a setup for their classic routines that they perfected from their days in burlesque as stage comics, their director Charles Barton was the first comedy director to incorporate the three camera setup instead of the one camera setup on film to match their timing perfectly, since he was a wonderful collaborator, another film that I highly recommend for spooks and chills is The Time of Their Lives (1946), being one of their most expensive films of that time.