It might be easier than you think for the OP to qualify for good bonus cards. For many years, I used one or two credit cards, spending little on them and carrying no balance. Fortunately, one of those cards was an Amex Platinum so I at least earned some Membership Rewards points--and because I didn't even notice those, I didn't blow them on something stupid, like Sony headphones for 100K points that might have instead got me a TATL biz class seat.

Some people are just dead set against credit use--many of them older than you think. In the OP's case, he's indicated that he worked as a consultant for a firm for 10 years and has been out on his own for another 10. Flown 750,000 miles in his lifetime, with 250,000 in the last ten years. Those facts suggest the OP is probably 45 years old at least and could easily be 60--and the child of parents out of the Depression era who would have beat on the lesson that credit was bad. Age, experience, and income history will more than make up for a lack of an extensive credit history.

If this is the case with the OP, he should realize the advice here is good. When I stumbled on FT, I was just like the OP--dead set against CC apps and skeptical that you could do things like apply for a Citi AA card--and then apply for another one 65 days later. Well, you can't quite do that for the time being although lots of people cashed in with the Citi AA Exec card this past spring, and I'm sure that at some point, there'll be another offer that is similar even if not with Citi or AA.

OP, you don't need to carry a balance on your credit cards. And the quickest way to accumulate miles/points for airline/hotel programs is credit card bonuses. When I got here four years ago, I had a little over 40K in AA--almost all of that earned through more than four years of paid leisure flying as my work does not generally require me to fly more than once per year.

I now have 475,000 in AA, 375K with BA, 200K in US, 225K in UA, 100K with Southwest, and shortly will have 55K with DL. Other than BA, I haven't flown a paid flight with AA, US, UA, or DL since joining here. With additional balances with the Amex Membership Rewards program, the Chase Ultimate Rewards program, and SPG, I have additional points that can be transferred to airline programs.

I don't note these balances to brag--lots of folks here burn more than I do and still have larger balances by far. But, it's an indication that the game is really not in the air any more. As others have noted, 25K of flying per year won't get you much (although with the right tickets, it can get you an elite level with BA which can translate into Oneworld status which then gets you benefits with AA and US). To fly up front, you'll probably need to either buy tickets for premium seats or earn enough award miles so that you can redeem them for premium seats.

The most efficient way to earn those miles is to go after CC bonuses. Pay off the balances each month. Learn enough about status levels in various programs so that if you see a plausible way to earn status you can go for it, but otherwise, accumulate miles. And instead of avoiding credit card spending, find a way to run every bit of your spending through a card. I suspect between personal spending (and I'm including bills and other payments that you might make as well as spending for dinners out, gasoline, clothes, and other daily spending) and your business-related spending, you can probably earn in excess of 100K in some miles or points program even after you've earned all the signup bonuses you want to apply for. That's only one overseas RT business class flight per year--but it's one you're leaving on the table currently.

You'll have to read and research here, but just decide that you have a new hobby--traveling in a bigger and better seat and making airline travel a much better experience than it is currently. Good luck!