I lost 61 pounds. I now weigh 144 at 5'7". Waist is a little over 28 inches. Can I now worry about my bike weight?

Actually, I'm not worried about my bike weight. I am shortly going to build up a CF frame (PedalForce RS) that should be quite a bit stiffer in the BB than my steelie (Colnago). I expect that the difference in stiffness and geometry will make a bigger difference than the weight change will. I am expecting a 3 pound difference between the two. The Colnago weighs in at 20. The PedalForce will probably come in around 17.

Lots of heavy stuff going on it. Cheap Al seatpost I scavenged off another bike. 8sp Campy Mirage also scavenged. Open Pro/Chorus hubs for wheels. When I can afford it, I'll upgrade the groupset to 11sp Chorus, get a different saddle and post, and the wheels to something more aero.

That said, many of us would benefit more from strength training, better cardio, and weight loss than from a lighter bike. I'll see my biggest improvements from climbing steep hills and riding distance at slightly higher than comfortable speeds.