If the amount of the coins I hoard increases my income, why would I ever spend them?
If I need to acquire coins in order to get income why would I bother with the currency in the first place?
While there may or may not be valid reason to do this for security it is absolutely senseless from an economical perspective.
Look at it this way: If you want to generate StakeCoin, you can do one of several things:
1. You can buy some, and invest them (e.g. lend them for X% weekly interest).
2. You can buy and run mining rigs, and pay for electricity, cooling and operation.
3. You can buy some coins, and "lock them into the blockchain". This helps the network security, and as a reward, you get to generate new coins.
Why is option 3 so bad, compared to 1 and 2?
This option enabled people to participate in "the mining game" directly, while in other coins you have to either
A) Dedicate large quantities of your time to understand how mining works, download miners, optimize hardware, etc... this is for specialists, normal people won't do it.
B) Mine-by-proxy - you can buy mining bonds ... but then you're trusting a 3rd party, who might be corrupt/corruptible.
StakeCoin is about allowing every "common Joe" to mine-by-proxy ... without a proxy.