Everywhere I have seen it done around here (DFW) it looks bad. Most of our fences are WRC and have a lot of spike knots in the pickets. Those knots don't char like the rest of the wood and it looks bad to me.
Your not going to extend the life of the wood either (if it's cedar.) A well maintained WRC fence will last 30+ years. Rot will not be the issue (rot occurs when water/moisture is trapped against wood for long periods of time and western red cedar has natural decay resistance) with a fence like it is with siding on a house because there is no where for moisture to get trapped.
Cedar fences fail because of rotten posts (why everyone uses galvanized posts now) or from movement of the pickets (warping, twisting, bowing.) Usually movement happens because moisture is being absorbed and removed unevenly from the wood. A good wood sealant will help prevent the moisture content from changing so quickly. The ends of the boards are where moisture is absorbed and released the fastest, so spraying is a lot easier for an existing fence.
Most contractors around here use ready seal. It's an oil based stain and sealant. $125-150 for 5 gallons that will cover 5-600 sq feet. Spray it on with a pump sprayer and back brush with a deck brush (I use a carwash brush from Home Depot.)
If you like the darker look, Ready Seal has a burnt hickory color that is right up your alley.
I have seen shou sugi ban done right at the AWFS. It's a Japanese art that is akin to making sushi. When done with the right skills and materials it's awesome, but taking a torch to a fence is to shou sugi ban as rolling a piece of catfish in Rice Krispies is to sushi.