We all know it's a great film so instead of me going on about that or how average the cover looks(!), I'll talk about what you're spending the extra £'s on, the Blu Ray conversion.... There have been a number of older films that have been put on to Blu Ray which, simply, have been very poor (see my review on Bullitt (another Warner title FYI)). The point of Blu Ray should be to showcase the very best in picture and audio quality that is currently available. Thankfully, this title has converted very well. The picture quality is exceptional, it makes a 28yr old film look very recent. Jack has never looked so maniacal! And again, the audio quality just brings a whole new experience to the film, adding an even darker edge than you were previously aware of.
I'd fully recommend the Blu Ray version of the film, top marks.