Motul is better mostly because it hold up to higher temps which is a must for the track or the fluid will boil over. The problem with race fluids like the Motul 600 (which I also use) is that is is supposed to be completely flushed every 6 months or it can damage your braking system (lines, master, seals, etc).

For the street, stock fluid is fine, but if you are going to flush, a Castrol GTMA synthetic is better without any side affects

Lines will generally make a more noticeable improvement in brake feel. However for the street, the biggest thing is just upgrading pads. The rest is marginal gains for quite a bit more money and effort. On the track its all a requirement.