What's 'overrated'?
I think dragon is roughly the worth of an outer turret. I would never willingly trade one of our outer turrets away to get dragon, but I would get dragon rather than take an enemy outer turret. Maybe even rather than getting an enemy inner turret. Absolutely I will always want to take an inhib turret over a dragon. Cracking the base is extremely important, those inhib towers are much more than just 'a tower'.
As for throwing at dragon or baron, well, nobody goes into those fights planning to get aced and lose the objective to the enemy team anyway.... but mistakes happen. If you could know the outcome, I'd say it's worth giving up a kill (but not multiple kills) to secure the dragon. It's obviously not worth giving up a kill to -not- get the dragon though, and very obviously even pros can't see the future, so I'm not a big fan of steal attempts other than with ranged skills.
I'm also not a big fan of trying to take dragon or baron with no wards. I do like to have wards peppering the area whenever dragon is up so that when the enemy tries to sneak a solo dragon, you wait until the dragon is almost dead, and then dive the hapless fellow killing him and taking the dragon away from him. It's really my -duty- to do so, as a helpful league player, I need to teach him why he should have wards before putting himself in an exposed position at low health while contesting a valuable objective. (Not to say I've never snuck a solo dragon myself ... but I always have wards at my back when I do.)
Dragon certainly isn't the be-all and end-all of the game, but it -is- a valuable objective. Those buffs are not huge but they are -permanent- (5th dragon aside, but then 5th dragon -is- a big buff.) That makes them pretty valuable. The 2nd/3rd/4th dragon buffs are kind of small on their own but if you add them together they make your team faster moving, faster pushing, and faster at taking turrets. That makes it easier to out-pressure and out-rotate the enemy team and get into their base - and you can't win the game if you don't get to the enemy nexus first no matter how many kills you get out on the map.