Have you looked at Neufert or Architectural Graphic Standards? I believe there is an angle to all the seats so everyone is a little skewed and stairs andexitscan be straight. Also, look at fifa website or olympic committee.

http://www.skyscrapercity.com/showthread.php?t=715478 I can't add this as a link from my phone, butlook at thefifa document in there

In real life they add or subtract seats to fill in the amount of available space. And vary the width between the seats to make the aisles seem to be uniform in width. Get in touch w a rep for stadium seating. Answering these type of questions is what real architects do-you are learning that the design of the entire structure can be driven by the size of the seat...

Establish how wide the aisles need to be and where they go. The width of the seating areas between aisles is a function of comfort and fire codes.

Then, fill the space between aisles with as many seats as you can. Space the seats equally. Stadium seats are usually mounted on rails. Sometimes they are mounted on individual posts.

Start at the bottom and work your way up. As the seating sections get wider, from time to time you will be adding seats.

Sometimes the layout will look a little strange, especially if you have small radii.

The seat width will affect the total seating count. Most developers will want to have narrow seats so they can sell more tickets. In real life, you will send your plans to the seat manufacturers, and they will come back with layouts that maximize seating.

thankyou so much everyone. your comments helped me a lot to go through my problem in an effective manner. 
as after a little arrangement of seating i think my aisles will have smooth profile till i get to the row where i can add one seat by squeezing all the seats in that row together. otherwise with all the other rows, ill add seats with increasing space between seats (from bottom to top). it can increase the comfort ability of the seats at the back.
or the other solution i thought was:-
if i place 4 chairs less in each row than the number of chairs it can hold and instead add a bench having capacity for 4 people squeezing in together wouldn't that be good? that way instead of loosing 2 chairs per row on the side of aisle, i can have a bench adjacent to the aisle and wont be loosing any capacity, plus will have as smooth aisle profile as ever.

what do you think?
 

Don't get too caught up on the seats, the real problem lies in establishing the correct sight lines, or at least the most ideal ones you can.  

the standard sight lines are obtained already as i have provided 3" rise in my second tier. plus i have started off with 1' riser in the first place. the maximum angle achieved is 26 degrees and not more than that anyway.
why am getting too much worked up in seats is because i was wishing of providing the maximum seats in circular form as most of the stadiums having circular form either have irregular aisle profile or have space in between seats as they go up. whenever we start off with a circular form the first thing that comes into mind of any person is 'a lot of space will be wasted'. I wanted to rectify and prove that circular forms can be used in a better way as well.

also, since this is a small stadium with a capacity of not more than 4000 people, i don't know what else i should be concentrating on except for sight lines and seating. :/

I would strongly recommend the literature that can be found on the Hussey Seating website.  They have some great resources about designing for the proper sightlines, comfortable seat and row widths, as well code related info.  Great Revit families too

For what kind of sport would a circular stadium be optimal? Certainly not football, basketball, soccer, rugby, lacrosse, field hockey, track and field...