A 194 bulb fit fine in my trunk on my 05, try throwing a normal 194 in there as a test.
The front sidemarkers don't flash, I have 194 LED's in there with clear corners and they look great. I may try to wire up a switchback that flashes in there soon to match the front switchback turn signals. The front turn signals are the only ones that need resistors as far aa I know, a 6-ohm resister inseries with each bulb.
I've notice the same with interior dimming^ I believe a capacitor and possibly a resistor in line could combat that. They're just so sensitive to voltage fluctuations, the stock dimming circuit just isn't "fine tuned" enough to dim them cleanly.
As for other interior lights, they wouldn't be worth it to do as then the dimming will act erratic if they aren't already LED's of some sort. The only place I'd think of switching for LED's is possibly the climate control cluster since they burn out much too often.
