Fantastic! Now you know you can do it - use the next century as a training goal next season. The fact that you did your first one solo is great. However I am like you , anything more than a metric solo and I get bored, a century with a group however is great. You will probably add a couple of mph to your average as the group helps each other along both phisically and mentally.
Since you hail from Rochacha your season must be winding down just as mine is about 200 miles east of you. I am resigned to doing most of my riding indoors until next April. Then it is start all over again - although next season I want to try an early century - never done one earlier in the year than July and there is one here in early May. My goal is to stay in shape enough to make that. Keeping the rear-end saddle ready will be the hardest part of that equation.
As far as the canal ride goes, I am typically swiming upstream of this crowd when they are on thier way from Scotia to Albany as my house is 1/2 mile from the bike path. There are a lot of cyclists that do this ride every year, a real mix of people. There is one real steep hill near my house that a lot of the folks will walk up, but from what I have read of your ability you would havn no trouble topping. I am usually headed west, and they are coming east. I have looked into this ride as well. Looks like fun. I thought I might load my bike up on the train and then ride back with the group. The price tag has held me back.