Lots of different strategies here and nearly all of them depend on your ownership style. There are many different types of ownership styles. I will get into a few of them below, but what an owner does with his minors typically depends on his ownership style. The descriptions below do not single out anybody and by no means do the below encompass every type of owner. These are just some trends that I have noticed.
Ownership Style 1 -- An owner that does not care about his minors and it is obviously apparent due to having the absolute minimum amount of players at each minor league level. These type of teams usually don't win many minor league games and may often times have guys that are fatigued below the 80 level by the time the season ends.. One of the first Worlds I was in had a long-term successful owner that punted the draft every year, but always had money to get the best Intl player in the pool. Since Intl players have baked in development, he would put them in AA or AAA and would have them in the MLB within a season or two. He may have missed out on 3-5 points of extra points of development by not making any minor league playoffs and missing promotion bumps, but when he was getting the best intl player every season, it really didn't matter. So, he didn't need any minor league system because all of his guys were so close to MLB ready, that filling the minors with players was a waste of time and salary;
Ownership Style 2 -- An owner that has a reasonable amount of players at each minor league level to avoid fatigue and injuries and compete to make the playoffs so his true prospects have a chance at more development in the minor league playoffs. This can be a guy that drafts HS or College talent and develops them with a decent coaching budget at each level. Another owner that was a good blueprint for me was in my first World as well. He had comp picks nearly every season. He also let guys go once they hit 30. He rarely signed guys long term and when he did, they were always HIS top tier guys. Since his teams were always young, he always had money to get one of the top Intl guys every single season. Since he always had comp picks and signed the majority of his draft picks, he had to have good coaching at each level. He also tried to win at each minor league level so that he gave his true prospects the best opportunity to obtain extra development in the minor league playoffs;
Ownership Style 3 -- An owner that spends an extra 2-3 million every season on minor league free agents and nearly maxes out every minor league level with players. This nearly guarantees that each minor league level that he focuses on will make the minor league playoffs barring an injury catastrophe or other owners having a killer class at a certain minor league level. This owner will also have a decent coaching budget like the Owner#2 above. However, this owner may get even more obsessive (i.e. if the owner has more pitching prospects at a level than he does hitting prospects, he will recruit bench coaches that have pitching ratings as opposed to bench coaches that are well rounded or have batting stats). This owner may also keep his true prospects on the bench and have them come in in the seventh inning via player rest in order to avoid injury. This owner may also keep all his true prospect pitchers in his bullpen in order to get in the most games, avoid fatigue and avoid injury. This owner is me. I spend a bit more than the average owner on my minors. Not because i care generally about my minor leagues winning, but because I exclusively focus on drafting HS players and developing them for four seasons. In order to avoid injuries, I sign minor league fodder during free agency so i can have my true prospects come off the bench during the season and just get in the game for three innings or so. Also, by signing the best minor league free agents, my minor league teams compete in the playoffs and my true prospects get the extra development without the extra fatigue;
Ownership Style 4 -- the World Jumping owner that trades nearly all of his minor league talent in order to win now. I have seen this multiple times, but I will use an example of an owner that we had in Glavine a few seasons ago. He came into the World by taking over a team that had just made it to the World Series the previous year and had great young talent. He proceeded to sell away his farm and even traded away the Wolrd's best young CF because the player was not playing up to his ratings during that season. He ended up winning the World Series that year and that left the World afterwards. He had some lame excuse, but the real reason he left was because the guys he traded for had expiring contracts and he had no farm. An owner like this not only doesn't care about his minor leagues, he doesn't care about the health of the World or the health of the franchise that he took over. All he cares about his padding his stats.
There are many other ownership styles that I can bring up, but this post is long enough. The gist is that you can run your minors how ever you see fit. There are many ways to build a successful franchise. However, be aware that certain Worlds have private world rules that prevent you from having super fatigued guys or penalize you for not winning enough games at the minor league levels.