Soooo I've got a few mods up my sleeve. First, did the reset button mod. Cut and filed the screw almost completely flush so there won't be any accidental presses.
Then I swapped out the d-pad & the contact pad underneath it with the ones from the RS-90. The d-pad sits at a higher profile & isn't indented in the center, which I prefer. The contact pad is a lot less spongey, definitely more crisp. D-pad and case required ever so slight trimming to fit (I just used a file). Also installed the glass screen protector while I was at it.
Last and most importantly, I made the shoulder buttons suck significantly less with a really simple fix. I build mechanical keyboards and had some extra springs laying around. Slotted one in between the button and pcb and boom, working shoulder buttons (TAKE NOTE FACTORY lol). Tried a bunch and these 125g ones felt the best. Now the buttons have actual depth to them and well.. spring back up. Worlds better and super simple. Ideally I would entirely swap out the shoulder buttons with tac-switches (like the RS-90 has), but for a non-solder option this is great.
NOW, take note of those two very prominent pads on the bottom of the PCB. They look like they might be for a left sound channel, but I wasn't able to confirm this. They're even marked +/- on the front side. There is plenty of space in the case there to mod in a second speaker. It might also explain why the volume dial is at max volume with only 1/4 of a turn. If the board was originally designed with two speakers in mind then essentially the one speaker is getting the power of both. The DS-Lite has excellent speakers that are basically the same size and exactly the same electronically as the current one. I'm thinking of picking up a set to see what I can do with them since replacements are so cheap.
ALSO, I believe I've found a huuuuuge battery that's ideal for replacing the small one, should be a super simple install (well, it'll still require case modification, and probably doing without the external SD, but hey).
One thing I haven't seen mentioned (that should be fairly easy to add) is qi wireless charging. You can get those little stick on coils for phones which should be fairly simple to integrate into the back of the case.
Once I have some money I'll order up the parts & fire up my soldering station.
Cheers! =]