Well, I've used the Conti 4000s for years and have had no issues. The only flats I've had were from me not watching the road and actually slashing the tire with sharp objects (twice in 9 years). Of course, I get my tires from various internet sources and they cost a fraction of the retail price.
I haven't really upgraded much. I got a Terry Falcon saddle 3 years ago, when I got my Kuota. I actually switched out the fancy carbon ergonomically correct bars for cheap, aluminum Specialized wsd bars that have a shallow drop and are narrow enough for me. Even though I have a very light bike, I don't care about the bars; I'm not racing. That's about it. My bike came with a wireless computer, which I really didn't want, since the previous ones I've had always conked out or gave me weird readings. But this one is OK. Oh, and I have a headlight I recently bought, since I have been doing some very early morning rides.
Instead of upgrading, I bought another bike to tool around on! I bought a pannier, 2 lights, a blinkie, and a cheap computer for my Jamis.