Personally, if I were planing to keep the bike 8-10 years I would invest the money in a new bike. For one thing, most bike shops will give you some sort of warranty on a new bike and sometimes a free 6 month adjustment tune up. I definitely think that carbon is worth its price. I can't say the carbon bike added a lot of speed to my rate although it did improve it some but the ride is definitely worth it over the miles.

As for riding in groups and riding alone, I think you have to figure it out for your self. I rode solo for years and found that I had a hard time really motivating myself. Yes I was getting in the miles but I was on a plateau. I started doing tours as a way to Plus it is a long term investment in your health,safety and sanity. learn to ride with a group and for the socialization. For the past three or four years I have been riding at least one a week with a group, mostly for distance, but it gives me the incentive to push myself on the days I ride solo.