I'm a very big braid advocate, but rivers especially shaped my opinion. It just has too many benefits to ignore and use it as main line on both, spinning and casting gear, but I think there is a learning curve, too.
First, I like the responsiveness and lack of stretch. Especially while fishing current seems where current changes direction, speed, or intensity, I like knowing that the fish won't likely out run my hook set or allow the current to botch the tension so long as you pay attention to my second point.
Two, braid floats. This is a curse and a blessing. The blessing is that it allows you to watch line as you would with a fly rod. The curse is that wind, changes in current, etc can all cause bowing in the line, creating slack and effecting your drift. I'm more recent to fishing with the fly, but it's helped my fishing with braid also in the sense that I've learned to better place casts (when possible) and also the importance of learning to mend line (for this, I actually favor longer rods on the river than most kayak guys).
Three, it allows you to alter your leader pretty easily to match conditions. Fishing grass lines in moderate current? It's easy to tie on 4-6' of InvisX. Fishing nasty boulders and snaggy snags? You can easily prep a leader of 12lb Hybrid which is d**n near indestructible in rocks and wood. Do you want some stretch for treble hooked lures? Pick up a spool of Cortland mono that normally fishes like a bungee cord. It's a nightmare for long hook sets as a main line, but as a 5-6' leader it adds a little functional stretch.
Four - it saves me a fortune. If I can get a solid 2 seasons out of a spool of braid and only use 4-6' lengths of leader line, spools of mono, floro, copolymer, etc last d**n near forever so long as they stay dry, cool, and relatively dark.
Five - With a good connection knot, I have very few knot problems, even with microguides on most of my rods and I just use simple double uni knots.
For river fishing, in 90% of applications, I'll take braid over anything else.