I'd like some comments on a dilemma I'm having at the moment about the economics of bikes, I guess.

I currently ride a Giant Avail 3. The 8spd cassette and the Sora shifters leave something to be desired. Otherwise, I like that bike. I've looked at upgrading it to full 105. That would run about $1000, by my estimation and poking around. I could get a 105-equipped bike for not a whole lot more than that. The Avail 1 (same frame) costs about $1300, plus the cost of pedals. From a purely financial standpoint, it's better to see if I can get $500-600 for my current bike, then put that cash toward a better-equipped bike.

Here's where it gets murky. For graduate school, depending on where I go, I'd like to get a hybrid for use as a commute/errand bike. I'd use the Avail, but she'd likely scream "STEAL ME!", being a road bike, and as a grad student, I'd have nowhere secure to put it. That merits another bike, which might run me up to about $500 (that's the most I'm willing to pay for a bike that I'm going to lock outside). The other thing is that I'd like something with room for a rack/panniers, and I don't want to have to keep taking things off and putting them back on, so this plan requires having a "fun" bike and a "work" bike. Selling the Avail would mean that I need to eat the cost of two bikes. I also have no idea what I'd upgrade to. I'm bouncing between the carbon Synapse, the CAAD 9 Feminine 5, and the Avail 1. I think buying the Avail 1 would be silly, because it's the same frame with some better parts on it--I may as well upgrade the key parts and leave the rest. That leaves two very different bikes. I'd test them out, obviously, if I were to purchase a new bike.
Finally, there's a bit of emotional attachment to my current bike. I know you all would get this a little more than my BF would (it's a machine to him). The teal is unusual and pretty without being girly. It's my first road bike...I think you all know what I mean. I'd like to keep it, but the practical side of me gets in the way.
Thoughts? Suggestions? What did those of you who have upgraded (parts or bike) do, and why?