I had a Panasonic AX200 720p PJ for a while and loved it. Seriously, it was awesome. Not sure if you'd notice a difference just with the resolution increase to 1080p but I know the 1080p models will be better in regards to contrast and actual picture quality so they are better, but since they are a lot more expensive they want to be.
You have to ask yourself the same question I asked myself last year. If you are looking at say a £700 PJ and are happy, then look at one costing £1,500 is the more expensive one £800 better? Then start to work backwards until you find the sweet spot.
How many movies are you going to watch a week? or how many hours playing games are you going to do? I hate gaming on projectors as they are too big for me. We watch one movie a week so for us spending anything over £500 is silly which is why I managed to find a second hand one pretty cheap.
Try and work it so when the times comes to sell it on you have got your moneys worth.