I think most people would say no but I say you definitely are missing out.... best to save that boost for your second or even third character IMO.
What I mean by this is that the leveling process (which itself is fast- going from level 79-80 takes the same amount of XP as going from 44 to 45 in this game) gives you an opportunity to just head out into and explore the zones doing whatever looks cool, and figuring out which areas of the map you really enjoy. You could do all this stuff at 80 but on most of the lower-level maps, XP is the primary reward (and you can level up even at level 70 in a level 30 map for example), so the impetus to do so once you're already at 80 is a lot less, and you'd be missing out on some of the best stuff in the game.
Once you have spent a bunch of time in a zone (100% completion, seen a ton of its dynamic events, etc.) it's a lot less fun to run through it a second time. If you open up most of the world on one character, the 80 boost is a lot more sensible on an alt.
Granted if the exploration aspect is of no consequence to you and you just want to try high-level stuff like Fractals, the big world bosses and map events, and raids, then go for it.
