Can somebody tell me how much BeoVision 7 32'' type 9311 with BL7-1 could be worth in mint condition? The set is about 3-4 years old and not much used.

Probably not as much as you'd expect. Lifestyle have a 2008-model that has sold for £3995:

http://www.lifestyle-av.co.uk/details.asp?sectionId=1&productId=3754

How many people would want a 3-4 year old BV7-32? I guess you'd get around £2700 privately or £1400 as a trade-in from your dealer. I wasn't offered a great deal for my BV7-40 MKIII, which is just over a year old. Some dealers didn't want it at all!