Just sold/traded mine after a year and a half (Great Game!) But have some strong opinions on this one. I actually put together a video on LEDs last year using LOTR as an example available here
I personally love and fully recommend COMET LEDs, but would not get the kit on this one. I'd recommend one of two options:
1. (~$30). Just replace the GI with LEDs. If you do this, I recommend the "Comet Retros" in sunlight for this pin. There are a few exposed lights in the game (like at the left lamp) and if you put 2 SMDs in those spots you'll see spots in your eyes after you play. The Comet Retros in sunlight are fairly close to what you would get if you you had just incandescent, but maybe 25% brighter with much less heat. You could also throw in a trough light for another $5 (easy LED strip... 2 alligator clips and glue strip)
2. (~$300). Do step 1 above but add color matched LEDs for the inserts. 2 SMD LEDs with color match and "Natural white" for the white inserts. If you change the inserts I highly recommend the LED OCD board as the machine electronically dims the lights for an effect and LEDS without the OCD board will recreate the effect by "flickering"... which can be almost seizure inducing.
3. If you do change out incandescent for LEDs, buy some "bulb condoms" in green to cover the upper left "Path of the dead" lights.
COLOR DMD or LCD:
I strongly recommend the LCD in Stern games... I think it looks better in here, and note that on the color DMD itself you can change how the pixels lock to either blend them together, make them squares, etc. I personally recommend "Dots XL" on this one.
Speaker upgrade:
I did not upgrade my speakers on LOTR, but I did plug in an external sub. That freaking Balrog roar is great with an external sub. Find a garage sale sub and clip it in to the sound system. 10/10 would recommend.
Art Blades:
Those look awesome... get those. Those are very similar to the "Silly Old Elf" blades you can't get anymore and they add to the world under glass.
Other things:
Mine came with a bunch of mods I installed when I got it. If you have a hard time getting up the ramp by the time you get to "Destroy the Ring" you may want to look into some upgraded flipper coils or flipper fans, but other than what you have listed that would be my number one recommendation. The only mod I really wanted but couldn't find was the expanded path of the dead figures (look great). I like the Palintir mod (not required) and the mount doom and upgraded towers are also cool, but probably not worth the money. I put in the full cliffy set on mine, but thats like a 2 hour install. The best bang for your buck mod IMO on this machine is... the $25 "Win a prize from Chucky Cheese's" topper.
Have fun with your new game. It's great!