Must I bring up the tragic Sand line? I don't care who you are, there's no way you could get that to not sound cheesy. :p
I think there's a combination of things going on here, with the Force.
A) I think somehow it's been weakened by the unbalance of the lightside, so it isn't as powerful, putting it in it's 'sorrowful state'. This would also explain why the Dark Side would have become much more powerful for a single person to wield. Thousands of Jedi on the light side, two for the dark side. If we're led to believe that there must be balance, those two darkies would be insanely powerful.
B) Light Jedi only needed to use it as a tool. They weren't called in as first responders, Jedi were the last line of defense, the last people you call in. They used the Force as a tool to get the job done, because that's what they're job required of them. The Dark side is, or at least seems, inherently more powerful, both because of how it's used, and who it's used by, and what you do with it.
Lightside- We protect the good, fight evil, make things right.
Darkside- We sneak in, start spamming force Destruction, Lightning, Grip, Throw, and kill kill kill, slaughtering thousands of people before we walk out unharmed.
Which seems more powerful to you? That's why I think when Vader said "The ability to destroy a planet is insignificant compared to the power of the Force," he was saying from personal experience. He didn't need to destroy a planet, he himself wiped out all (read: most) of the Jedi by himself (as far as we know now). Even Vader used the Force as a tool, to destroy the Jedi, to destroy the rebellion, etc.
The Force is just a tool. It was used for different purposes. In the OT, you mainly saw the Dark Side. You saw that it was powerful, evil, it would destroy and eat and corrupt. In the NT, you mainly saw the light side of the force, the part that helps and heals.
Two uses of the same tool.
[edit- On the topic of streamlined ships:
I think the difference is that in the NT, you're looking at a government who hasn't fought a fullscale war in a thousand years. Ten centuries. That's a long time. In the OT, it's a warzone. You have battles and fights and unrest everywhere.
Look at the ships:
Star Destroyers: Giant lumbering ships with lots and lots of guns. Quite similar, both in function and looks, to naval Battlecruisers.
TIE Fighters- Built to be cheap, fast to produce, and have guns. Built for quantity, not quality.
X/Y-Wings- Financed by the few rich people in the rebellion, they were built for just the opposite, quality and not quantity. They wanted the fastest, heaviest armed, best armored bang for their buck. They didn't have the time, nor the money, to waste on making the ships look cool, have retractable weapons and sleek designs.
Mon Calamari Cruisers/Other 'Capital' Rebellion Ships- They looked like crap. To put it bluntly, it looks like a lot of them were thrown together for efficiency, because that's what they were. Thrown together warships, produced illegally, that had to be able to go toe-to-toe with the bigger Empire ships.
Conversely, in the NT, like I said before. They'd be at peace for a thousand years. They didn't need to worry about building the ships fast, because there was no urgent, pressing need for them to defend your latest base's evacuation. You could waste money on them, because they were legal, and mass produced to look nice. The Naboo ship was the Royal Cruiser. It was a luxury car! Not a ragged fighter that was produced for a few thousand credits in a week.
So I think a lot of people miss this, the fact that people are comparing ships from a wartime and a peacetime. During peacetime, people want to show off their new rides, and there's little chance of being blown up.
