Just to be practical here...
It doesn't sound like racing is where you're headed, and if you are mostly doing short local rides, you don't need a lot of bike. You liked your fixed gear steel fixie. Dude-go buy a steel fixie. They are cheap, ride great, provide great training and you can cut your budget to $300 or less. I would look for an 80s steel frame with horizontal drop outs and build one up. Trek and a ton of Japanese companies made perfect frames for this for decades and they can be bought for peanuts on Craigs. Heck, I've got a 56 cm modern cheap steel track frame I'll sell you for $100. Comes with most of the parts you'll need for a fixie including cranks and a rear wheel.
If you want to ride seriously, but recreationally, then it's time to spend some $$. A modern good carbon fiber bike with Ultegra or Dura Ace is what you want. Titanium rides really nice too but it will cost you more than your budget.
Race bikes are easier to buy because they are disposable. Any bike you have you're going to ride a year or two anyway and replace. This is where aluminum frames shine.
Most people buy way more bike than they need, because it's easier to buy than to ride. True fact. Look at that Trek. It's an awesome bike, and it's hardly been ridden. If it's your size you should buy it.
I have gone full circle. I don't race anymore, I ride almost every day of my life, and the carbon and aluminum(except 1 mountain bike) bikes are gone. My commute bike is...a steel fixie! I ride it 28 miles every day to and from work. My century bike is a steel custom with Dura Ace. To me as a 30+ year rider, steel feels the best over distance, though I have nearly pulled the trigger on titanium several times but I don't feel worthy of it anymore.
And BTW-lots of great steel frames still being made.
I agree completely that the only thing that matters for the riding you describe is fit. Not weight, not material, not components. If you're riding under 150 miles per week, don't waste a bunch of $$.
