Training & Nutrition - Strength to weight ratio

I am wondering if I need to add some more body weight to gain additional strength for my riding. I am 40 years old, 6'1", and weigh 157 lbs. It seems that when riding with a group I don't have the power to keep up with them on the flats when the going heats up. However, when the hills come around I can almost drop them all and I know I still have a bit more gas for climbing (thus I prefer the hills over the flats when group riding:)). Should I add a bit of body weight to help gain more strength for the flats? Will the extra body weight hurt my climbing abilities? Currently I can only sustain a 45 minute time trial at about 22 mph. Thanks for the help.

If you look at pix of professional cyclists, especially close ups of them riding at >20mph you will be struck by how skinny they are. Their upper body would be expected to be average in muscle development, about like a 14yr boy. But the legs, for most of them are NOT large, but the muscles are very well defined
From the front the legs look large but look again from the side and you will see they are not. Most notable example was the TdF mountain contender Michael Rasmussen, but all the TdF, Giro and Vuelta biggies had asthenic appearing legs. The fact that you can drop most of your peers on hills shows you have considerable basic power, what you need is interval training to improve your maximal aerobic capacity. More weight/muscle is not the answer.

Thanks for the reply and inspiration.