Whether to buy a new road bike or not?

[KyleB]

I'm having a hard time deciding whether or not to buy a new road bike.. I currently have a 74 Schwinn Varsity (12 speed bc I have a new back wheel). I really enjoy riding it and its built like a tank so I don't have to worry about something breaking or anything. I live in an area with so-so roads that aren't great for roadbiking all the time but they work. I have about $600 I could spend (but don't have to) on a new road bike at the LBS, possibly online. Should I go ahead and spend alot now, or should I just get what will suit me for what I need? I take really good care of my bikes, and kind of want to try out the new style of road bikes (STI shifters, 700c aluminum wheels, lightness, etc....) I'm just worried about the wheels not handling the roads as well as my current 27in monsters on my Schwinn, etc...

I mainly ride for exercise and leisure (want to go on some nice long summer rides), although I might get into racing or charity rides in the future...

Anyone have any advice? Any positive, genuine advice is welcome!

Thanks!