Gaunty, ER and mainwheel, agree with you all (as far as it goes - I am in no position to know whether DJ has the right spares inventory)
Certainly an aircraft operation should have a minimum of spares - but 5 bars worth is too much. At commercial spares lease rates that would cost you around $75k each and every month - plus the usage of them of course. Whether the $75k is worth paying is dependent on what not having such spares would cost - a very complex calculation dependent on many things, including failure probabilities, reputation costs, recovery costs, how tight the fleet plan is (spare A/C), maintenance turn times and capacity, direct delay costs etc etc.
In my experience, having lots of spares is a false panacea - Murphy's law always strikes, and the one vital part you actually need is not even in the $5m parcel, or else is not in the place it's needed.
Far more important (imho) is to have access arrangements to spares pools (rather than holding them yourself) at major ports on your network. The access costs are usually pretty cheap (even if the actual loan charges are not). And no reason why this shouldn't get by an intense scrute.
It's all part of the art of inventory management - not a simple thing at all. To use mainwheel's example in a different way, how many servos do you think carry a spare pump? I'd guess maybe close to zero. I'd also guess that most carry almost no pump spare parts at all - effectively on-condition repair.
I'll still stick with my assertion that a good clean (reputable, reasonable dispatch reliability up above say 98%) 737 operation can be had with a little over $1m spares holding. DJ with its fleet should have a multiple of that, but certainly nowhere near $5m per tail.