I know each market is different, but I've found over the years that paying a little bit extra for a letter has a far better return than a postcard.

I'll end it with this about Harrisburg, and I know it could be said about any city, but I feel that Harrisburg is extra unique in this regard....it is very block by block! 

I had clients go the Designed to Earn the Energy Star route over LEED a bunch.

His rent covers most of the PITI and my wife and I cover the rest (+ extra for Maint, Vacancy, and Capex).

So, if you are going to invest there, I think it best to NOT assume it will continue to boom as it has over the short term, make sure the deal makes sense today, and has some extra "insulation" to cushion you in case it goes bust so that you are not forced to sell or lose the property then.

Would the money you use to pay them off earn you more if you invested it?  

This is when extra payments make the biggest difference.  

That may help you in terms of finding deals and perhaps making a little extra cash.

Specifically I am looking at buying either a 3 bedroom 2 bathroom house and renting out the two extra rooms or buying a duplex/triplex and renting out the extra houses.  

Even if you just throw the extra money in the mattress it is available to you at no cost.