There are enough reviews of the different versions so I won't go into detail. Just two things to add that may be helpful to UK viewers:
1) This is not a Hollywoodised Christmas. It was a low-budget film produced from an excellent script and very true to life. I spent the first 26 years of my life in England and have no problem whatsoever relating to this U.S. version of Christmas. Family interactions, kids' Christmas obsessions (every kid of my age at some point got or wanted a gun for Christmas or birthday), Bing and Ovaltine on the radio, everyday kid life, it's all here. The schoolteacher I could swear is taken straight off one of my early teachers and both dad and mum contain so much of the best (and not-so-best) of most people's parents. It's a film that withstands repeated viewings and has long been a Christmas standard in our family.
2) As outstanding as the film itself is, the extras I've seen on various versions aren't up to much. After your jaw has dropped at how much Peter Billingsley still looks like his 13 year old self, there's not much else. As much as the film eschews corn and cliche, the extras revel in it. So if you want to replace your old tape, go for it, but if you're looking only to update your version for extra entertainment from the add-ons, I personally wouldn't bother.