This from a guy who suffers from upgrade fever as much as the next guy:

Stick with your original budget. You'll still get the joy of riding, the pain of getting in shape and the challenge of raising the bar on your goals and expectations...this is 95% of cycling. And you can upgrade down the line.

Yes, others will correctly point out that the cost of upgrading later will be higher than getting the same components already on the bike. But in the larger scheme of things I think it's wiser to stay with your original budget as best you can.

Just some friendly advice, since you asked.