Anything that is remotely investment grade has ten offers on it within days and there is always an investor willing to overpay.

Because the grade, ( C Average) I have increased vacancy and collections from 12% to 15%)What are your general thoughts?

The slab on grade concrete foundation is designed for compression and uses minimum rebar to control shrinkage and temperature cracks.

The water company also told my Property Manager that my building has this issue every year and we found out that the water line was installed only 12" below grade and not below the frost line. 

Selecting what to do has much to do with you, your ablities, goals, credit, money avaialble and personal preferrences, there is no better property per se.I suggest you study your tail off, get very good grades and stand out among your peers first and not be so concerned with investing now so much but pick up the basics and techniques a little as you go.

If its a slab on grade home no real need to worry.

-Walk the surrounding neighborhoods to monitor the quality of each neighborhood-Get an inspector to provide a report on each property for proactive maintenance: termite, AC servicing, grading dirt, finding hidden leaks, etc. 

CF, it becomes more speculative than investment grade IMO.    

So a single factor like a water treatment plant isn’t going to make or break the deal you need to grade the area as a whole based on the comps.

Older still and you might well have clay pipes.Much of the older cast iron sewer lines are nearing end of life ... especially if buried in wet soil or poorly graded so they sit partially full most of the time.