I've been flying about 20,000 miles a year recently. This year, I made a few discoveries that have made a big difference in my travel experience.
1. Global Entry
If you're not familiar, this is the US Customs program that gets you automatic TSA PreCheck so you don't have to take off your shoes and remove your laptop at security. You also get a separate screening line at most airports.
I'm late to the game on this one but I got the $450/yr business platinum card. If you're willing to do a little setup, the perks more than pay for themselves. I find the most value in the lounge access, the $200 in airline credit, in-flight internet passes and Amex will pay for your Global Entry signup. It's paid for itself several times over for me.
I did the Business Platinum, which is a bit cheaper but doesn't include the Uber credits. I don't use Uber because of their ethical issues, so I saved on that.
This is a $39 / yr mailing list that emails your fare sales and discount fares, including some premium seats. I have seen some mistake fares, too. Recently a ~$200ish round trip from Dallas to Melbourne, Australia popped up. Pretty amazing.