Being a member of a club is what you make of it. My club has trail/road runs 3 times a week, and a track session once a week. People are free to pick and choose if they wish to join a run. There is never any pressure to attend any meet ups. Most clubs are friendly, and I'm sure operate along the same lines. But I can highly recommend the camaraderie of training in a group, especially for longer distances. Sometimes the only thing getting me out of bed on a cold winter morning for a long run is knowing there are other people there as well, and they will encourage me all the way. I really can't think of any con's to joining a club.
The problem I find with plans is that they are 'one size fits all'. As a 49 year old woman, my training needs are going to be very different from a man in his twenties. I managed 3:50 at VLM this year, but did not follow a plan as I find I need to factor in recovery from my lsr. I agree that you need a mix of lsr, threshold and speed work, each week, but real life gets in there as well, so fit the runs in around everything else. Plans also do not take into account if you pick up a slight niggle and want to take it easy for a day or so to recover.