I bought a hybrid when I first was getting into cycling. I thought at the time that I wanted a road bike, but they were expensive and I didn't have any real experience with them. I wasn't sure if cycling would be a "fad" for me or not. So I took the hybrid and rode it a lot.

Six months later, I had done a lot of research and I felt confident in buying a nice new road bike. I knew I was making a good decision. Plus, having two bikes allowed me to go with a more aggressive roadie, and keep the hybrid for commuting to work and running errands, etc.

Best part of waiting and researching while riding the hybrid is that, six months from now, the road bikes you're eyeing right now will be cheaper. I'd hold off buying a more expensive road bike until you know its really what you want. Especially if you're on a budget. You can be just as serious and get just as hard a workout on a hybrid as you can on a road bike. As you said in your post, you're mostly interested in fitness and weight loss at this point. The hybrid is every bit as good as a real road bike for that purpose. All that matters for training/weight loss purposes is the amount of power you put to the pedals. On the road bike, the same amount of power will translate to faster velocity, which is cool in its own right, but going faster for the same amount of work doesn't help you get fitter in the least. No real sense in going all out right away, at least not in my opinion. But then, everyone's entitled to his own.