"A rocket engine is one of the most effective--if not efficient--means of turning fuel into power there is."

That can not be true.

What I roughly calculated I believe is somewhere in the ballpark. If you used a rocket engine instead of a car engine and you wanted to drive 1000 miles straight at 50 mph or 200 mph, probably the best any rocket engine would get is about 1 mile per gallon [whereas a car with a normal engine could easily get 35 miles per gallon]

"I've read that a single SSME, which would fit on a large flatbed truck, generates eight times the power generated by Hoover Dam."

Ok but it's burning a lot of fuel- something like a swimming pool worth in seconds. Oh, here is exact quote:
"If water, instead of fuel, were pumped by the three Space Shuttle Main Engines, an average family-sized swimming pool could be drained in 25 seconds."
And your quote is:
"The energy released by three of Pratt & Whitney Rocketdyne's SSMEs is equivalent to the output of 13 Hoover Dams."
SSMEs

Or:
"Shuttle Tank. Gross Mass: 750 975 kg (1 655 616 lb). Empty Mass: 29 930 kg (65 980 lb)."
Meaning the weight of the the LOX and the LH2 is 721,045 kg.
The 3 SSMEs have burn time of: Burn time: 480 sec.
Now the SSME aren't at full thrust all the time, but if I ignore that and simply divide 721,045 kg by 480 seconds I get 1502 kg per second [of both H2 and LOX].

Now, without the solid boosters the Shuttle can't get off the pad, each weigh: "Gross Mass: 589 670 kg (1 299 990 lb). Empty Mass: 86 183 kg (190 000 lb)."
The fuel and oxider weigh: 503,487 kg. So both weigh: 1,006,974
They have burn rate of 124 sec. So they burn 8120 kg per sec
So the Shuttle at lift off is burning about 9 tonnes per sec- and very roughly the two Solid boosters are providing at least 4 times the power as the 3 SSMEs.
Also:
"Liftoff Thrust: 25 751.600 kN (5 789 190 lbf). Total Mass: 2 029 633 kg (4 474 574 lb)."
http://www.astronautix.com/lvs/shuttle.htm

And:
5 789 190 lbf) minus 4 474 574 lb equals 1,314,616 Then divide 1,314,616 By 4 474 574 which equals .2938 Therefore at liftoff the Shuttle accelerates at .2938 of a gee [2.879 meters per sec per sec].

In first 20 seconds from liftoff the Shuttle burns about 192,440 kg of fuel and oxider [ a 11th of it's total mass]. At the 20 second mark, the Shuttle weighs 2 029 633 kg minus 192,440 kg which is 1,837,198 kg [roughly 4,051,010 lbs] It's acceleration at this point is .4291 of a gee [4.2 meter per sec2. To make this overly simple the average of 2.879 meters and 4.2 meter per sec2 is about 3.5 meters per sec2.
Distance = acceleration1/2 times Time squared. So at average of 3.5 acceleration in 20 second of time the Shuttle travels a distance of 708 meters. And 3.5 m/s times 20 seconds means the Shuttle is traveling at 70 m/s [252 kph or 156 mph].
If at the 20 second mark all power were to shut off, the Shuttle would decelerate at 9.8 m/s/s which means that in about 7 seconds the shuttle would stop going up. In first second after power cutting off, the shuttle would get to about 773 meters, next second 828 meters, then 873 meters, 908 meters, 933 meters, 948 meters, and then 953 meter then at around this point start dropping.

Now, getting back to your first quote:
""A rocket engine is one of the most effective--if not efficient--means of turning fuel into power there is."

A rocket may be an effective way of turning a lot fuel into power- I don't think there is any other type of engine/vehicle that consumes 9 tonnes of fuel a second.
"Worlds Largest Passenger Cruise Ship - Royal Caribbean
The ship consumes approximately 28,000 gallons of fuel per hour."
http://www.funonthenet.in/content/view/363/31/

Say gallon of this fuel weighs 6 lbs, so that's 168,000 lbs [76,366.6 kg] per hr. Divide by 3600 and you get a mere 21 kg per second.

Now, even though obviously a Pipelauncher does not exist, it could deliver more power than any existing rocket and would give you this power at a fuel efficiency better than any car. On the order of 10 times the power and 100th of the fuel comsumed per power delivered. In case you ever wanted to know why bother mentioning such a idea.