Comparing a pro with the mods listed to a stock LE isn't a good comparison. Most of this mods such as: mini arcade cabinet upgrade, upgraded speakers, external subwoofer, shaker motor are practically mandatory to get the full Tron experience. So if you look at the cost of an LE you really should add the cost of those mods as well.
If you have a pro and an LE with all of the mods listed earlier and the only difference from pro and the LE is: the color changing vs static color rampos, moving recognizer, drop targets, chrome accents, and daft punk multiball then thats a more valid comparison. I love my LE but I think a pro all blinged out with the eye candy will stand up well againt an LE for 2-3K less in cost.
If I had to pick the biggest bang for the buck upgrade for either version of Tron it would have to be adding an external subwoofer. The Daft Punk soundtrack and the games sound effects just sound awesome with one.
I agree that the LED's under the inserts on the LE look much better than the regular bulbs on the pro. There are 2 Tron pro's in my area on location and they rather look dim and dull compared to the LED's in the LE. My only compliant is that the light cycle inserts are not yellow enough. They have a lime green look to them that I wish was more yellow.