To answer Elderly's original question, I started upgrade of BD7 to 8 at level 53 and finished BD10 at level 56. My IPH was about $8k when I did BD9 to 10 run. I am a completely free player...I don't camp, but my work schedule means I don't have much time to play, so I level up slowly. Most of my leveling up is due to events.
I knew at level 30s that the BD10 was the ultimate goal, so I Set my sight early on and planned for it. I build up a strong army with decent weapons that would not become obsolete around level 50s. I invests in high output economic buildings like level 2 manors, lenders, and got my silos to level 9, taverns to 8, leather works to 6, pottery to 5. I kept a rather low profile with only 120 allies and raid/attack only profitable targets.
To breed dragons, you need more deliberate allocation of resources as each dragon cost $13k. I have been adding about 15 each day. With an IPH of only $9k, the only weapons I am buying are the Bandit Leather (2/8) and Staff of Thunder (3/4)...this combo cost only $$1540 but adds more points per gold than the dragon. I am doing more pvp now as players at lvl 50s are becoming more lucrative, and I have no fear of retaliation now. I am focusing on upgrading the pair of merchant caravans as these have the best ROI and provide me with $2000++ every hour.