I don't think the area around Scarborough Town Centre is run down or crime ridden. Borough Dr. and the residential neighbourhood to the south are actually very nice. The mall is currently undergoing a massive renovation and really, was not that bad to begin with.
Yeah, the area around there is fine, but devoid of activity. IOW, I'm not sure there is such a thing as "downtown Scarborough". However, the mall really did need the makeover. It wasn't absolutely terrible, but it was looking pretty tired IMO.
The northern half of Scarborough, including STC, is anything but run down...it's far too new. Anyone who thinks it is run down either needs to get out and about the city more or is from the 905.
When I first moved to Toronto I didn't quite understand the anti Scarborough sentiment, because I was a downtowner and the only places in Scarborough I had visited were north of Ellesmere. It's pretty boring up there, but well kept.
The parts I'm not impressed with are areas between Kingston Road and Lawrence. They look run down. I now live south of Kingston Road which is very nice, but the north of Kingston Road run-down-ness bugs me since it means that Kingston Road itself has crappy shopping. Hopefully that will change in the next 15 years now that it has gotten rezoned.
If anything, home prices in Scarborough could be set to rise over the next decade because they didn't explode in the recent bubble and because the entire borough is becoming a real bargain. It's not like some kind of racial war is going to erupt.
IIRC, north Scarborough has been getting some significant price increases, along with the rest of Toronto. Same goes for Scarborough Bluffs. I'm not so sure about the area surrounding Eglinton though. However, the point to remember is that regions of Scarborough were cheaper to begin with, so any price increases, even if comparable percentage-wise, might not be as mindblowing as some of the more expensive areas.
The region surround Eglinton has the most potential for price increases in some ways because it's very cheap now, but I'm not optimistic. If the Eglinton X-town gets cancelled, then there's not much incentive to put more money in there IMO. What I suspect is that north Scarborough will continue to be solidly middle class, Kingston Road will get more money, and the developments in the St. Clair region will improve that area as well.