Wait. Are you really doing that badly? You are converting, I'd guess based on your data, about 5% of your download base, which is actually very reasonable. But you are losing like 25% immediately, so your conversion of active users is actually quite higher, maybe 7.5-10%. You may be focusing on the wrong metric. I would consider instead focusing on getting downloads higher.

Additionally, I wouldn't offer the bundle packs but instead sell everything individually. I read a great article a few weeks ago on making in app purchase work for games. (I write productivity apps.) One of the things they said was have lots of ways for people to spend money. Only a small percentage of people spend so you need them to spend a lot. The comment was that the best performing games are generating upwards of $50/spending user, all via in app purchase, all from like 1-2% of the download base.