Personally I think it's difficult to define 'too far' in a world that is as broadly spectrum-ed as this one.
Some folks here are hairy panty wearers and may consider a wig to be 'too far'.
There are the feel good illusion chasers like me, for me 'too far' would be any permanent change to my outward physical appearance that heavily favours my crossdressing.
Then you have transexuals, and for these folk sometimes even hormones are not enough and they choose to undergo appearance changing surgery.
It's really, much like everything else here - Different strokes (no, not Gary Coleman LOL)
-x-