I've seen all kinds dude....too bright, not bright enough....weird colors....cool white when it should be warm white...I've seen a million LED jobs and they're all superior w/ regular bulbs and sporadic LED additions. Super or Ultra Bright LEDs in the inserts? Gives me a splitting headache in about 30 seconds of play. A Cirqus Voltaire at PPE had Super or Ultras in the inserts and GI...in a way it has the opposite effect and makes the game seem "darker", as the brightness concentration is so intense it focuses the eye on the hot-spots and almost silhouettes out the rest of the playfield.
LEDs on new Stern games? Looks worse than regular bulbs because #1 - Stern games are bright as hell anyway, #2 - Stern games use multi-level brightness FX which LEDs can't handle without strobing/flickering. Spider-Man for instance, I tried some LEDs in the blue inserts (I'll give you THAT, blues generally look better w/ LED)....and it just doesn't work because the villain inserts have 3 levels of brightness based on how many villain battles you've won, and the LED doesn't work right with that function.
Back to STTNG...I saw an STTNG at PPE with LEDs...looked DARKER because the G.I. LEDs don't offer as much light spread as a normal bulb. Know where I put LEDs on my STTNG? Under the Klingon ship...they aim DOWN at the playfield, brightening up a darker game, but they don't shine in my eyes. To me, this is the best use of LEDs....spotlight type situations. Any game I have with spotlights I use HP-5 LEDs from Cointaker....they significantly brighten the playfield without the drawbacks of being in my line of sight, flickering, ghosting, or not functioning the way the game was intended. Hell, I've got a 13-LED flasher in Homer's head on TSPP. It's awesomely bright but because Homer's head is thick plastic, it doesnt fry your irises out.
OK, if your games are in an arcade...that makes sense from a maintenance point of view...and if the place is brightly lit, I suppose that counteracts some of the intense brightness.....but I generally play my games in the dark in my gameroom....they're bright enough!