Well Xeno these are some pretty relative questions. I don't personally believe you would see a noticeable difference if you used the same speeds but ECC vs Non ECC however, technically speaking you would have more error correction thus more stability. As to if that would stop programs from crashing, that would depend entirely on the reason the programs are crashing. Do you have reason to believe that RAM is the source of the program crashses? I would certainly recomment checking your event logs both Application and System. Overall, unless you have specific reason to suspsect the RAM's ECC nature being the issue, I certainly would not assume it was the reason and I don't think unless I had that reason it would be worth the fairly significant expenditure for ECC vs Non ECC.
One reason is a 4gb chip of 1333mhz is about 90 bucks vs a similar stick of Non-ECC is about 23 bucks. Pretty significant difference.