I think you will be fine. I actually was debating between the two. I want a low cost projector for my bedroom ( my good 3d projector is in my theater room) The 550 is actually 50 lumens brighter. IMO the brighter the better. That way you won't have to watch in total darkness but LED lumens are brighter than bulb lumens so both could stand up to a little light. The main two things that jumped out at me are sound outputs and contrast ratio....the 550 has a 10,000:1 contrast ratio which is way higher than the 3000:1 ratio on the 500.....also with the 550 it has audio outputs...I know thats null and void if you hit your receiver first but some people want to hit the projector first...if thats the case then the 550 will be better because the 500 does not have an audio out. I feel as though overall the 550 will work out better for you....the higher contrast and higher lumens should translate to a better picture for your movies. But one thing to keep in mind the 550 has an external power supply so you will have to hide a power brick.....the 500 on the other hand has the supply built in so you only have to worry about hiding a regular power cord. Not a brick, Hope that helps.
Center: RC-62 (need to upgrade)
Display: Optoma 1080p 3d projector with 120" Screen
Misc: PS3, PS4, Xbox 360, Xbox One, Roku 3, Harman receiver, Wii, Blu Ray player