WAY TO GO!
i started riding this month (once last week, once today. prob tomorrow), so i don't have the breadth of experiences you have. not sure i'll be riding in the rain or not... agree with most of your other observations, esp #1.
biggest reason for riding was also exercise. my knees and hips have demanded i stop running (last fall), so this gives me an outlet. if commuting becomes more frequent, i'll probably add panniers as well. last week i brought a change of clothes, etc, the day before, and took everything home the day after. obviously that doesn't work if you bike 2 days in a row (ok, it could..), but kinda cuts out Mon and Fri from the mix.
it's been fun. i've got LOTS of people asking about it - one has already started (last week as well), and we'll probably both ride in tomorrow. that will have to be the 1st time we've had 2 bikes at the bike rack at the same time!!! One other has said he'd probably do it as well (he's traveling this week, so no chance of 3 tomorrow). most people asking live too far (>20 mi) to try it, tho. still, it's given me a bit of "rock star" attention lately :)
car commute: 17 min, bike: 40-ish, on an 8.5-9.0 mile ride (i take a longer route home to avoid some traffic). also no shower.
as for my wallet - i just take my drivers lic, debit card and some cash and rubber band them together and carry in a pocket.
also need to remember to bring my work key fob.
CL Fuji Pulsar (road bike). will prob need new tires after the summer.