How much effort do I put in my security for Android In App Billing?

Question

I implemented In app Billing in my Android application. I pretty much followed the sample (Dungeon) application to get it working. It seems to be functioning fine as of now. I now need to decide how much effort I should put into the Security portion.

I do have a server that I could use to implement the Security.java stuff. I also am currently using the standard PurchaseDatabase implementation.

As of right now I am thinking of just encrypting the .db file with a device specific key, and leaving Security.java alone.

My thinking is that my app is a pretty niche app, and I am not expecting a lot of hacking on it. If there are some people that put in the effort to save a couple bucks (each item to be purchased will only be $1), so be it.

I guess I am looking for opinions on what other people think about this...it seems there is no 100% secure implementation...just implementations that make the hacking not worth the effort. Have other people seen a lot of hacking of In App Purchases?