Different methods work for different people.
Depending on the airline, you can buy coach tickets and upgrade them to business class with miles. Or you can buy business class tickets and upgrade them with miles. Not all airlines charge hefty fees for doing that, and typically the mileage is far lower than the award mileage. You have to know the rules for the upgrades in order to use this strategy. Each airline is different, and as I mentioned, some charge hefty fees for international upgrades, and some don't.
Some people also buy tickets from consolidators that can be much cheaper than the retail price charged by the airline.
The other way to do it is to get top tier status in an airline program, and some of them come with system-wide upgrades that can be used on certain discount fares. Depending on the airline and their available promotions, you might be able to attain that status by flying on mileage runs, which will entail some cost to you, but the benefits of the status, the miles earned (including tier bonuses, etc) and the system-wide upgrades may be worth much more than the money it costs to attain status.
Different things work for different people. The first step would be to find the right airline program for you based not only on cost of flying, but on the cost of international upgrades and how they charge taxes and fees for those upgrades and what fare classes can be upgraded, and then concentrate your flying and credit card usage so that all your miles are going into that program, either directly, or indirectly through the use of alliance partners. Doing so will also give you a head start on getting EQMs on that airline towards attaining status with that airline program.
There are several people on TUG that have 1k status on United. Some of us have attained and maintained that status via use of mileage runs. Those are the people that tend to fly overseas in business and first without paying business or first prices. I'm sure you can do it with other mileage programs also, but I'm not as familiar with them as United's program.
Personally, I've been overseas twice this year. I went to Bangkok and Singapore in May in business class at coach prices (using VDB vouchers for most of the fare) and to Singapore in July using miles in First. I also have another trip planned to Thailand using miles.
Both United and American had double EQM promotions this year, which made it very easy to reach 1k for next year. Unfortunately those promotions are over now. You have to keep up to date with the stuff if you're serious about it.
Miles and points can also be purchased, sometimes at a discount. You have to also plan that out and determine if the price/point or mile being charged is worth it for you. Planning comes into play because, as with Marriott, you may be limited to the number of points you can purchase in a given period.
I think the other thing to remember about the value of those promo points from the developer is that most of us would never actually buy a first class ticket to Europe or Asia if we didn't have those promo points. You pay for them one way or the other, and on paper or at the sales presentation, the sales presentation always makes sense, but I don't think they do in a true value proposition.
However, I recognize that my method of looking at these things is not the same as yours. Both of our methods are very subjective. So, if you think it's worth it to buy from the developer at developer prices, who am I to say it isn't worth it for you? What I can say with a very clear conscious is that for most people, the better deal is to buy on the resale market.