First of all, congrats on the weight loss and increased fitness. I'm on a similar journey having lost 45 lbs and toning up quite nicely from cycling and strength workouts at the gym. Certainly, working on the "engine" creates the most noticeable and cost effective improvement!

That being said, I found that the purchase of a bicycle dramatically increased my motivation and opened up a whole new world to me. I was going to wait until I dropped the first 40 lbs before I made the purchase, but my local bike shop owner encouraged me to get the bike sooner than later. That was some superb advice, and after losing the first 20 lbs I bought a Specialized Sirrus Limited. The second 20 lbs came off much quicker, and my enthusiasm for fitness, good nutrition, and overall health has skyrocketed!

So you might find that the new bike could provide that same sort of motivation. Or perhaps just upgrading some parts on your existing bike would do the same. Certainly, the narrower tires would provide some mechanical efficiencies that would be noticeable and appreciated. The three bikes that you are looking at would be a measurable upgrade from your Fisher, but as my bike shop owner said to me last week: "Before I spent $500 to save 200 grams, I'd reduce the weight of the engine by 10 lbs for free and get much better results". Sometimes I hate that guy.....