The Secteur, in one year, has earned a reputation as a pretty nice bike. Upgrading your bike at this point in your cycling career would be total bling, not function. If you can afford it, it's your money. Just be aware it won't make you go faster or longer.

Personalizing your bike is another matter. Most of us get a new seat almost as a matter of course. This does make a difference because it influences how long you can comfortably ride. Tires also influence this; plus, getting flat-resistant tires gives you a measure of peace of mind. I'd keep your wheels for the time being, and agree with the poster above who recommended you take them to a good local bike wrench to make sure they're correctly tensioned and trued.

If you don't live in a really hilly area, I'd consider changing out the cassette for something like a 12-27. TANSTAAFL applies here; the wide range of the 11-32 cassette means that you have big jumps on each shift. Going to a tighter cassette gives smaller changes in cadence on each shift.

When you first start cycling, you get better pretty quickly, but then improvement levels off. If you want to keep getting better, you need to organize your training. Joe Friel's Cyclist's Training Bible is pretty much the standard, with Chris Carmichael's The Ultimate Ride also popular. Wait until it's raining too much to ride, and start reading.

If you don't already have one, you need a cycling computer. You can get a good quality, basic one for ~$20. If you're going to get serious, take some of that money you were going to spend on wheels and get one that incorporates heart rate and cadence. You'll end up spending ~$250-$300, but then this is one of those things that can be moved from bike to bike when you finally do get another one. You can usually download the data from them to track your improvements and see where you've been, since most of them are GPS-enabled as well.

As to weight...unless you're REALLY lean, you'll get more improvement from losing that spare tire than from anything you can bolt onto the bike.

Good luck!