How much does the bike really matter?

[zatar]

Apologies in advance if this isn't the right forum... I couldn't really decide which section to post in.

I just joined a cycling team this year and have my first road race tomorrow! My team members have really helped me to build up my bike handling skills and I'm excited to start racing. I've seen a lot of improvement so far and even shaved 5 minutes of my time on a ~13 mile course.

The only lingering concern I have now is my bike. I ride a 2007 Marin Portofina with pretty much all stock components. My parents bought it for me, as an 18th birthday present from REI, and I've really enjoyed it so far. I got it professionally fitted in late November 09, but have already outgrown it (thanks to a very late growth spurt!). I imagine the pain that has developed recently could be alleviated by raising the saddle, but I haven't done so yet.

I have started to look at new bikes, since I now have a (very weak) excuse to do so. I am wondering if it's worthwhile to make the jump to a more expensive bike? I looked at the Specialized Dolce Sport and Specialized Allez Elite at the bike shop today. I'd like to keep my cost below $1000, but might be able to spend $1500 - $2000 if it would make a huge difference.

I think I'm just feeling a little discouraged because I feel like I work really hard to improve myself as a rider, but then, I handicap myself by not splurging on a fancier bike. I was especially frustrated with myself last week because I felt I did really well at my first time trial (20.55mph, 194 avg HR), but my time wasn't very good. I didn't use any aero equipment and raced in my heavy-duty winter training tires. I think part of this was an unconscious way of shifting blame from myself to my bike, and I am upset with myself about that. It's like I don't give myself a chance at success, because that opens the possibility that I could have everything I need and still fail.

I think that's a large part of why I haven't splurged on a fancier bike already, but I'm tired of being that way. I think I want to go for it and buy a lighter bike. I noticed that I have no problem riding with teammates when they're on their rain bikes, but when they have their race bikes out, it's sometimes hard for me to keep up.

I guess all of this rambling can be condensed into a few questions.
1) How much does the weight and quality of the bike really matter?
2) Is it worthwhile to spend a significant amount of money on a road bike with nicer components (Shimano 105 range, probably), or should I save my money and continue trying to focus on improving myself only?

Thanks in advance for any advice and/or input you guys might have!