About your penis tissue changes -- wrinkly, veins, shrinkage, skinnier -- I experienced the same thing towards the end of my 11 months on the drug and still am 20 months off, but I haven't tried anything that could help with it yet (been waiting for things to recover on their own) - but I am going to try some stuff very soon (within a week or two -- natural supplements only).
Best of my knowledge this type of thing is a combination of factors -- low androgens, prostate shrinkage due to finasteride, possibly low Nitric Oxide.
For example, see this study:
http://www.asiaandro.com/1008-682X/5/33.htm
Low DHT via Finasteride can lead to tissue fibrosis/Peyronie's in a small percentage of men, which can be further compounded if you have low T after coming off the drug. So you need to verify your hormones and see if your Total Testosterone, Free/Bioavailable Testosterone and DHT are low or normal.
If you have low Total/Free/Bio T and DHT, you need to work with a Doctor to get those up via treatments like Clomid, hCG, Nolvadex or TRT. Or try natural supplements first like Tribulus, Tongkat Ali and the other stuff listed in the Naturals section of propeciahelp.com.
Other things that can help with fibrosis/Peyronie's are v**** before bed (stimulate nocturnal erections -- see this study:
http://www.propeciahelp.com/forum/viewtopic.php?t=572 ), L-Arginine before bed (increased Nitric Oxide), Vitamin E (natural, not synthetic @ 200-400iu/day -- do research on Peyronie's Disease treatments on Google), Acetyl-L-Carnitine, Pineapple juice (Bromelain), Ginkgo Biloba and Korean Ginseng.
The other thing to keep in mind is since Finasteride acts by shrinking the Prostate, and since the Prostate is involved in seminal fluid production and plays a role in erections/nerve stimulation, that your Prostate may have something to do with this too... you may also want to investigate the possibility of Prostatitis. Read this to understand the importance of the Prostate for male sexual health -- when its removed, sexual dysfunction, shrinkage etc occurs due to nerves/blood flow being cut:
http://www.propeciahelp.com/forum/viewtopic.php?t=521
I'm in the same boat as you and I know it sucks but over time things do improve somewhat. At least now I can get hard and have sex whereas when I quit I couldn't even get it up.
Do your research via the Studies section on propeciahelp.com and you should have a better idea of how to proceed with things. Blood tests and a Penile Ultrasound would probably be the best next step.
To all the naysayers -- this man is suffering and is in the exact same spot I was 16 months ago. It is not in his head and if you get these types of physical side effects, you will know they are real.
Best of luck Jon, and don't listen to these juvenile forum noobs who try to discount every single side effect of Finasteride just because they haven't experienced any (yet). Let the hard facts and scientific studies be your guide because they are the truth, unlike these guys who have nothing to backup their claims.
Mew.
and maybe a lil shorter 
