I ride a scissor on 47c's but it's not really for 'tricks' - I just like being able to jump over and off stuff. I use it off road too. And for me the only reason for having a fixed bike as opposed to a street mtb is that I like being able to sit down probably. On my scissor I've got full leg extension and a nice hi bar position.
yes
The only reason I wouldn;t ride a jump frame with a mega seat post is aesthetic - I think it looks shite. Plain and simple.
yes
http://lunaextrema.files.wordpress.com/2011/11/yao-ming-meme1.jpg
http://www.lfgss.com/picture.php?albumid=747&pictureid=12710
The reason I prefer Scissor on 700c wheels is that I ended up with a tendonitis on a smaller frame and a herniated disc.