Ideally your rents will cover most/all of the expenses and lower your cost of living which will then accelerate your savings rate. 

Ideally, your rents received will cover most/all of your expenses which will lower your cost of living and accelerate your savings rate.

It is a great way to accelerate the growth of your retirement savings.The refinance will need to be non-recourse. 

I've managed to purchase two investment properties over that time, but want to accelerate my learning and growth.

Once you've gotten one under your belt your learning will accelerate.

There are some strategies that could be overlooked including "accelerated depreciation".

As others have mentioned, you could still pay more towards the principal on your current 30 year loans and pay them off at an accelerated rate as if they were 15 year loans. 

If the seller is an owner occupant, he may have an LTV much higher than any investor can obtainThe main benefits to a seller is that the transaction is quicker than a buyer obtaining new financing, and that he may get a higher price because the buyer does not have fees associated with obtaining a new loan and the buyer may pay more for greater leverage or pay more if he can’t qualify for a loanThe downside to both is primarily that the buyers equity can be wiped out if the note holder accelerates the note, further the seller now has liability on a note secured by a property he does not own.

@Marie Fries Thank you so much Marie, I really appreciate you taking the time out and helping me prepare and to accelerate this process for me.

Read books, listen to podcasts, read blogs, be active here or even get a mentor who will accelerate your progress.