I just completed my LED upgrade and wanted to thank infinitiandbeyond for the original post which took most of the work out of doing the upgrades.
I started about 4 months ago and changed out the front parking lamps, the trunk lights, backup light, license plate light and door courtesy puddle lights. Because I didn't want to permanently modify my new M35S I stopped short of doing the interior lights. Well, when this post was revived it motivated me to complete the job.
First thing I did was pop the DIY 30 SMT W's out of the trunk lights. Because they were just loosely floating around behind the diffuser lens you could always see that the LED panels were crooked. I put a small amount of clear, high-tech polymer adhesive/caulking on the edges of the LED panels and stuck it to the diffuser lenses. Now the LED's panels are lined up nice parallel to the top and bottom of the lens. Probably a little AR, but it looks more professional now.
Next to the interior. The rear 16 LED - 3175_16_SMT_W were plug and play. On to the front dome/maps lights. I took rsg123's suggestion of using an array and used the same 30 LED - DIY 30 SMT W I used in the trunk with the supplied adapter. You can get similar LED's on ebay but V-LED's gives me such good service I just ordered them from there and had them in 2 days. Note, if you use the DIY 30 SMT W from V-LED's with the supplied adapter they won't work out of the box because the polarity is backwards on the adapter. You need to gently pry or pull the 3-pin connector off the adapter and flip it around 180º and push it back on then they will work fine.
While the look of the LED's pressed up against the diffuser lens is fine for the trunk I really didn't want that look in the dome lights. To get around this I just used the existing post in the housing (the one infinitiandbeyond ground off in his installation) to "mount" the LED panel. To do this just used the same polymer adhesive I used in the trunk and stuck the back of LED panel to the bottom of the post. This recesses the array to about the same depth as the original bulb and give a much more diffuse light instead of seeing the 30 individual light sources as you see in the trunk. Plus, it is completely reversible if you ever need/want to go back.
I didn't bother with the footwell lights since I have never noticed they were there plus I forgot to order any LED's for them. Maybe later.
Anyway, the interior is really bright and really white now.