OK, sounds like LCD projector's have a lot of issues, so I'll avoid those for sure.
My living room would probably make a quieter bedroom for me than the current bedrom as it doesn't have an adjoining flat next to it, which the bedroom does so I hear some noise through the walls. Below me the flat is the same layout, so if I made my bedroom the living room it might be a problem for the person below as well as the adjoining flat if they're trying to sleep though. Above me, the flat is a split-level with the first floor the living-room/kitchen/bathroom and the floor above the bedrooms, so it wouldn't make much difference to them. Another problem would be that if I swapped the rooms over, guests would have to go through the bedroom to get to the kitchen and it's obviously nicer to have the kitchen off the living room so you can check on cooking or make drinks and still talk to people in the living room. So I think all things considered, it's just easier to block the extra windows if necessary than swap rooms.
I think if there was likely to be a 1500 Lumens LED projector available soon for under £500 and that would give a great picture with the curtains drawn but not necessarily having to totally black out the room, just make it fairly dark, then I'd wait for that. It would be best if it would also be watchable, although obviously not great, for daytime viewing without having to close all the curtains but I could just keep using a small LCD monitor for that, although that would add an extra £80 to the setup cost. My concerns are that even if a 1500 Lumens projector does become available soon, it's likely to be nearer £1000 than £500 and that it may still be too dim to be used in other than a almost totally dark room, which can be a bit impractical when guests are round and have to be able to see their food and drinks to avoid knocking things over, keep moving around and getting up to get stuff from the kitchen, etc. I note what you said about "I can have a LED 12 watts lamp light that is simulated of a 40 watt regular light bulb in the back of the room" with your 700 Lumens rated LGPA75U, so it may be OK if I setup some lighting above the seating positions with a 1500 Lumens projector but probably still wouldn't be watchable with the curtains open during the daytime.
I probably could afford a LG Full HD Plasma but I've seen enough people warn me off LG I'm afraid, although just because their TVs have issues doesn't mean that their projectors do.
I'm going to take some screenshots of PC games at 1920x1080 and 1280x720 and check how they look in store on the 42" and 50" Panasonic plasmas with their 1024x768 resolution. The 50" will be about £120 more (including the 5-year warranty which is only 10%) so I want to check it will look OK from 7-8ft away, otherwise I'll probably get the 42", which will seem smaller than my 36" CRT as it will be 2-3ft further away towards the back wall but there's no point getting the 50" if I'm going to see the pixels from my seating position.