upgrade an already jailbroken phone

[otisore]

hello all, i'm currently using a jailbroken iPhone4 running on IOS4.0. i'm very happy with it outside of the few glitches once in a while, but i understand the compromises with a jailbroken phone. anyways, i just came across the Find My iPhone app in the Apple store and would like to install it, but it requires IOS4.2...so...my question is, if I upgrade my phone and jailbreak it again, do I have to reinstall (repurchase?) the Cydia apps and settings for all the apps? or is there a way to save all these and have them reinstalled after the new jailbreak? appreciate any help. thanks.