We had a sprinkler system at a house that we though had been removed, but it turned out all the heads, etc were just buried under gras and soil due to disuse.

Stack two up high with a desk underneath - with rails of course.

I'd put my money on the fact that they put the addition on spread footings without doing much to improve the soils under them. 

Large, transverse cracks are the larger worry, as they are more likely caused by differential settlement in your foundation (the soil underneath a portion of your foundation wall dropping, while the rest stays more or less where you want it - look for a "stair-step" pattern in your mortar joints), water trapping against (or worse, inside) the wall and expanding during the winter freeze cycles, or insufficient steel reinforcement - which is not uncommon with concrete masonry, particularly if the house is pre-1950s (ish). 

,Soil characteristics, vegetative cover, and status of mineral rights, andOther factors affecting value.For each comparable sale, the appraisal must include the names of the buyer and seller, the deed book and page number, the date of sale and selling price, a property description, the amount and terms of mortgages, property surveys, the assessed value, the tax rate, and the assessor's appraised FMV.The comparable selling prices must be adjusted to account for differences between the sale property and the donated property.

They are easy to assemble and will actually last.In a related tip, if you have the opportunity to tile underneath your cabinets DO SO.

I beg that you don't buy this POS since the only fix is to either bring the slab back to grade or throw crap tons of steel members underneath the concrete and create a diaphragm to transfer the loads correctly. 

Our ceiling underneath was lath and plaster, and very uneven.

It implies that the ground underneath dropped because it wasn't compacted when the slab was built, but I doubt that's the case. 

There's a screened in porch that's underneath the roofline that I could turn into a 4th bedroom rather easily.