Given that you will probably be spending a couple of year of your hard earned cash on the house, which will have to be paid paid back for the next 30 or so years, you are right to be very careful about where you buy.
I have found that areas which are nice and quiet on a lovely sunny day can become much more sinister and frightening places to be at night.
No matter where you are living at present, given the size of your investment, it should be possible for you to walk around the area of the house that you are thinking about at night. Do it on several different nights, including Fri and Sat. Are there many undesireables hanging round? Did you feel threatened? Would you be happy walking round at 1.00 or 3.00 in the morning?
Also you stated that you lived near Ballymun when you were in College. Living near Ballymun is not the same as living in Ballymun. Its one thing to walk around Glasnevin or Santry or wherever you were staying, but did you ever walk round Ballymun itself at night?
Murt
Murt