I only use the bluebook values as an extremely rough starting point for a couple of reasons. First, there are so many bike models/years/configurations out there that it's just a guide at best - people tend to anchor their perception of what their possessions are worth (price anchoring).
Second - bikes will last a really, really long time if properly cared for, so I don't even care so much if I pay an extra $50-100 for a bike that really fits me. Over the next two decades that's a puny amount of money. I know that's heresy on these boards, but....
Ok - regarding components... each step "up" gives you better performance, lighter weight and (to a certain level) more durability. That's because each groupset is made with better materials than the one below it. BUT - once you go above ~Shimano 105 durability flatlines (or even declines slightly)... those upper-end group sets are all about small savings in weight and slightly improved functionality.
For Shimano it goes: Sora < Claris < Tiagra < 105 < Ultegra < Dura-ace.
Sora is pretty much crap that goes on big-box store bikes for people who won't use them extensively and don't know better. Skip that.
Ultegra & Dura-ace are for serious racers with price tags to match. To be fair I've never had the pleasure of riding Dura-ace (out of my pay grade).
My advice is to stick to Tiagra/105. A great blend of durability (105 might actually be the MOST durable), performance and price. You won't look out of place lining up at the local bike race, fun-ride or long-distance charity ride on a bike with 105. Even hardcore competitive cyclists often have a daily training bike with 105 to grind out miles, saving their expensive race bike(s) with Dura-ace for race day.
Finally, more of a personal decision but your gearing can have two chain-rings or three chain-rings (the large rings near the pedals). If you climb steep hills you'll want the 3 rings (the littlest is often called the 'granny gear' and it allows you to keep pedaling even while going very slowly up very steep slopes). I've got a 2x9 on my road bike, but when I bought it I was living in an area with very few hills.
The cassette (sometimes called the cog-set) are the gears in back. Depending on the year of your groupset they will be anywhere from 8 to 11. Much older group sets had 7 or even 5. I've never worried much about size of my rear-cassette; IMO 8 is plenty for all but the most varied of terrain or the most serious of cyclists. Others will no doubt disagree.