I've never thought that sights would be useful in terms of aiming, but thought that a scope of some kind could help you see someone hiding, is that not the case?
My latest comments on sights:
http://p8ntballer-forums.com/threads/milsim-markers-poor-design-for-paintball.160993/page-2#post-1471785
You can see further with a telescopic sight, but get tunnel vision
If someone is hiding then you scanning an area with sights will give them more of an advantage while you are concentrating on a reduced view.
If you know roughly where they are and use a sight to look deeply into it then it could help, but then you have to be able to do something about it with range and accuracy if you need the sight to see them
The best things for fitting to you marker are:
A camera - but a gun camera as opposed to a head camera will get more ground and air footage
A torch - for night & indoor games - but be disciplined and keep the light off except for when you knowit won't adversely advertise your position or highlight teammates - eg room searches