Differences between bikes 10 years ago and now? I'm not too knowledgeable on high-end racing bikes, but I'm looking at getting a used Specialized Roubaix, and I was wondering whether enough significant advances have been made since 2007 to consider getting a newer lower-end model vs a 2007 S-works Roubaix.

Have there been any advancements that render bikes from that long ago obsolete at the high end?
You did not disclose the used price but that is most likely putting you in a mid range bicycle.

Drive train:
The information I pulled up the drive train is 2 x 10. Seeing more 1 x gearing now but 2 x 10 is in no way obsolete.  You can certainly get 1 x in mid range bicycles.  If 1x gearing is important to you then go with mid range new.  You are going to go from a high group set to a lower end group set.  I would take the older high end group set every time if it is in working order.

Brakes:
The 2007 has rim brakes. In the mid range you now have the option of disc brakes.  Do you want disc brakes?  Rim brakes are not obsolete and have done the job for many years.

Rims / Wheels:
You are definitely going to take step down on wheels. If the wheels are in good shape I would rather have older high end wheels.

Frame:
Frame, headset, bottom bracket are all modern.

Use case:
If you are not going to race you may select a different style of bike but the Roubaix is a nice versatile bike. 

Value:
You don't say the price but compare that price to the new bikes at that price. My experience is you can get some really good pricing on high end bikes as high end riders with the money want to trade up and get the latest and greatest.  Sponsored riders get a bike a year for cost or less.  According to Kelly the price in excellent condition is $1100 and that is a much nicer bike than a new $1100 bike in my opinion.  If they want $2000 US I would say no as then you can get into a lot more options new with a frame warranty and I would go 1x with disc and stretch it to $3000.  Wearables on that bike are $400.  

Risk:
As with any used bike you risk the frame is damaged and that is not always apparent.  But for the right price it is worth it for the wheels and components alone.