What version did you go for - H7 or D2S ?
You have valid point with trying the OEM lenses. Your 2009 car have better factory lenses than mine (2005 'fresnel' lens) and you have much better chance of achiving better results. Yes, its possible and should be fairly easy as dimension of projector are identical and lenses are easy to take out and swap. I would be VERY interested in results as I am having same issues on my retro E46 as you - I wish it had a bit more of spreadout light mostly in sides as I find the RFL projectors extremely narrow. Sometimes turning in unlit forest road is impossible unless I put foglamps on (see difference on the road with and without fogs, below)
I learned to live with it but it certainly leave a lot field for improvement.
BTW I dont find the signs "unlit", actually sometimes the other way around - when driving I can see that my lights make signs reflect a lot more than other cars (easy to spot by colour of reflection). I have them set properly (even maybe a tiny bit lower than I could) as I drive a lot on uneven country roads.
If you feel adventureous and willing to try swapping lens - please make sure you do a comparison shots.
just to show you differences in my case, see pics below with fresnel lens and clear lens. On the wall its easy to spot all light leaks and deformity of patterns, and you can immediately know if its gonna work or not.
