Build it up to break it down again

I have always been interested in Lego NXT. It seems like a really easy way to get into robotics, and programming. I have never really figured out how functional it is in the "real world" (whatever that means)
The other day a coworker was really pushing the idea on me telling me I needed to buy a kit because it was so easy to build things. Now I really struggle with the arduino most of the time, but I enjoy the struggle, and I know that if I ultimately build something then I can replicate it fairly cheaply. That is my issue with NXT. It is REALLY expensive. It is expensive for legos, it is expensive for a microprocessor, and it is expensive for the peripherals. I think I'm past the target age of these things, but regardless, I priced out how much it would cost for me to "replicate" an NXT kit with and arduino.

Here's the NXT specs fro the lego site (lightly edited for clarity)

# 3 Interactive Servo motors
# sound sensor
# ultrasonic sensor
# touch sensor
# light / color sensor
# 519 specially selected LEGO TECHNIC pieces
# 4 input ports, 3 output ports and 7 6-wire cords
# Matrix display
# Real sound speaker
# USB 2.0 and Bluetooth support
# Easy-to-use PC and Mac compatible interface
# Intuitive, icon-based drag-and-drop program "building" environment.

and there is this special offer
*Purchase 8527 LEGO® MINDSTORMS NXT and receive a FREE F9847 Bluetooth® Dongle.
The NXT kit 8527 will run you $249.99

Here is the breakdown for the Arduino
color light sensor $19
"Touch Sensor" Aka Pushbutton $2.99 (2)
ultrasonic sensor $$27
3 continuous rotation Servos $39
Microphone $3.79
Arduino Decemilia usb starter kit $65.00
protoshield ncludes a 10K potentiometer, 1K potentiometer, 2 small pushbuttons, 5 red diffused bright LEDs, one each of red, green and blue ultrabright LED, 5 100 ohm resistors, 5 1K resistors, 5 10K resistors, and a CdS photocell (new!). Also includes 4 pieces of 18" long jumper wire
LED MATRIX $6.95
All of that comes to $163.73 before taxes and shipping! $80 lessFor that you are getting a lot more functionality, and more applicable hardware knowledge. Granted, the "knowledge barrier to entry" is higher, but I think that when robotics are concerned, everyone is probably interested in learning just as much as they are in results. This is a pretty heady field. On the other hand I don't think there is any dispute in saying that the nxt is cool for kids to play with. My interest in this whole proposition is more because I am sick of people telling me to buy legos, when you can buy the real hardware for less. If your kid is either einstein, already interested in programming, or over 15, I'd say stay away from the familiar bricks.

Just for kicks, lets load up the cart until we hit our fabled $249.99 price tag!

...we can build up our electronics toolkit.
diagonal cutters $2.95
wire strippers $3.95
1 lb of solder $12.99
Basic soldering iron $7.99
...We can make some pcb boards...
PCB Etching kit $15.99
...We can even get an extra arduino, this time in a smaller form factor!
Boarduino $17.50
USB TTL-232 Cable for boarduino $20

In conclusion - I say go for the route of more knowledge, It's usually cheaper, more frustrating, and ultimately more rewarding. You don't even need to go the arduino route, you could go basic stamp, pic, or any other kind of chip! I think the only reason for an adult to get an NXT is the one that never gets mentioned - you can buy it "for the kids" and then play with it into the night...