I changed out the screen cover on my X3 this weekend with positive results. I now have no issues reading the screen outdoors. I can't take credit for this mod however, as I've seen someone else do this on HF 1st. That individual didn't use the same materials as I did though, but the net result was the same.
I used a replacement top screen cover (
NOT screen protector FILM) designed for a Nintendo DS Lite (I had a used one laying around from a previous DS Lite repair). It was about the right thickness, is made from shatter-proof and scratch-resistant plastic (probably polycarbonate), and cut easily with scissors.
Here's a example of the product:
http://www.ebay.com/itm/ZedLabz-rep...for-Nintendo-DS-Lite-NDSL-Black-/291678096912

You can find them on ebay (and probably aliexpress) of you search for 'plastic screen cover Nintendo DS Lite' or 'plastic lens Nintendo DS Lite'. Although they are getting harder to find as the DS is quite old now, many other things would work equally as well - 1/32" polycarbonate sheet, an outer screen cover from some Blackberry phone models (like the Curve for example), etc.
I would
NOT use brittle plastic, like from a CD jewel case, as that plastic scratches easily and cracks/shatters even easier. I would also not use plastic that is too thin, like the plastic used for retail 'clamshell' or 'blister' packages that many toys and items comes inside, because it won't protect the screen from pressure/cracking. Examples of what
NOT to use:


Anyways, once you have obtained a suitable screen cover, you just insert the edge of a disposable razor blade into the LONG edge of the X3 screen cover, and PRY it using the X3's aluminum for leverage.
The prying action is like what you would do when using a crowbar or removing a nail with the claw end of a hammer. You can also pre-warm the cover by gently heating the area with a hair dryer set on low (you won't damage the X3, but it will soften the adhesive & make it much easier to remove).

My screen cover came out with no damage to the cover or the X3.
There will be some adhesive residue left from the stock screen cover's double-sided tape. Clean off the residue using some Q-tips (cotton swabs) dampened with a drop of Goo Gone, Goof Off, Acetone, or nail polish remover (being extra careful not to drip any onto the OLED screen or down into anything electronic).
Cutting the new cover is easy. I laid the stock cover on top of the Nintendo cover, and cut along the edges of the Nintendo cover with sharp scissors using the stock cover as a guide. Make sure to round the corners like the stock screen, and test fit.
Once I was happy with the fitment, I glued the clear screen cover in place with a few drops of UV-activated epoxy (you can also use traditional epoxy).
Do NOT use super glue, because it will release vapors as it cures that will leave a white film on the inside of the cover and actual screen.
I could have left it like this, but I went one step further and replicated the black surround of the stock screen by trimming a scrap of flat black vinyl sign-graphic material using an xacto knife. Just peel and stick the trimmed piece of vinyl onto the outside of the clear screen cover and you're done. You can certainly omit this step and it won't affect anything. You'll just be able to see your drops of glue, as well as some of the circuit board through the new clear lens. The vinyl trim just gives it a little more professional 'factory-finished' look. Whether or not you do it is up to you.
Here's the final result with vinyl trim piece:
Don't worry if you mess up somehow (the cutting or gluing), because the Nintendo screen cover is large enough to make (2) X3 screen covers with some room left over.
Now, what kind of difference does it make with the stock smoked vs new clear cover? You be the judge:
The comparison photos were taken indoors with manual F-Stop and aperture settings (so there was consistent exposure from photo to photo, and no interference with the camera's automatic settings). There was no retouching of the photos at all.
I've already tested this outdoors. On the brightest setting, the screen is very readable in everything but the most intense direct sunlight (like at the beach at noon on a sunny day with no clouds). As we all know, with the stock screen cover on the brightest setting, the screen is not readable at all (except in the shade, when it is BARELY readable).
The new clear cover is still a little hard to read outdoors when wearing really dark sunglasses, but that's true of any phone/laptop/MP3 screen (with the stock cover the screen could not be read at all while wearing sunglasses).
Seeing how in the comparison photo, the stock screen cover at the
MAXIMUM brightness (16) is
THE SAME BRIGHTNESS as the clear screen cover at the
MINIMUM brightness (1), you'll start to get an idea of just how effective this mod is. If I had to estimate, I would say that the clear screen cover increases the effective brightness by at least 50%.
Another advantage of the mod is that because the screen cover is clear, you can turn down the screen brightness (especially indoors). This increases the battery life!
Total time from start to finish was 20 minutes (15 if you don't do the vinyl trim). Total cost is $3 for the Nintendo cover, plus free ($0) for a small 2" scrap piece of vinyl at any sign/graphics shop (or you could buy a larger piece on ebay for ~$1).
Enjoy,
- Slater