We always make the parents co-sign on the lease, therefore, if there is any excessive damage, we can go after the parents for repairs.

While your strategy is not within an IRA 12% seems excessive.

We would receive interest in excess of 15% a year and our investment was secured by collateral in the property.

Which is further exaggerated by debt sitting in excess of home values.

It seems everyone I talked to there was excessively overemployed.

We hard money lenders leverage our time and resources by allowing outside, passive investors to participate in our loans along side us - and we of course earn significant fees (mostly paid by borrower, but of course in some way sacrificed by investor) in excess of our return on our own capital.  

For example, I expect my portfolio to remain mostly real estate (>80%) until/unless I build a net worth well in excess of $1M. 

I have a job that I really enjoy, and am really just looking to supplement my income, and use my excess time wisely.

What are some ways to profit from it, without selling too much of it, or logging it excessively? 

As long as you are using debt wisely and not over-leveraging yourself, then there is nothing wrong with leveraging the excess cash you have now to fund your growth with additional debt .