I reckon joining a club is the best thing I've ever done. There are two main ones in my area - one is a bit snooty and all about the racing. From what I hear they are down to under 30 members and all bickering amongst themselves.
My club on the other hand are superb. I joined when I moved to the area about 3 years ago. They're super friendly, cater for all needs (there's slow rides, fast rides, long rides, short rides, mid week a chaingang, a mid week pub ride, time trials etc etc.
Aside from the advantages you list there are plenty of fringe benefits, for me at least. I find there's always motivation to get out on the bike, a different group of friends, plenty of people around to offer advice and help regarding bike maintenance. I've got to know the guys who run the local bike shops which means that a) I get better service b) a club discount c) occasionally a mates rate discount on top of the club discount! I started out as a strong-ish cyclist and was ok to go straight into the faster, longer groups. I had the intention of just doing clubruns and the odd sportive but after a year in the club it became clear that I quite liked competition and was encouraged and helped to start racing.
As for the bike - don't worry. If it's a good club there'll be no snobbishness. A woman started coming out with us about a year ago. SHe had this super heavy aluminium shopper/hybrid type bike. She was made to feel very welcome, and she's now got herself a Trek road bike but she wasn't exposed to ridicule. Equally we've got young lads who are desperate to get the latest carbon creation but simply can't afford it so they ride around on their dads' 30 year old steel frames. No one says anything, after all there are a couple of guys who turn up in winter on bikes that look like they've been nicked off the local vicar - we give them loads of stick but we all know they can rip peoples legs off if they choose to, regardless of the bike they're on!
Age, again, is no problem. We've got a guy who's in his late 70s who comes out with us quite regularly and there are plenty like him.
In summary, club cycling (with the right club) is a wonderful, friendly and fun experience. What could be better than going out or a ride in the morning with a whole bunch of mates. Stopping for coffee and cake and talking bikes, the Tour and having a bit of fun sprinting for hills and signs and getting fit at the same time. Join one! It'll change your life for the better!