Hi,
my wife and I rented there (sea view over the west pier) for 6ths at 1400 euro per mth - that was 2 years ago. I believe rents have dropped in the area since.
Dun L has good and bad... good places to eat (40 foot and a purple place behind the ferry terminal), good theatre, great walks on both piers, good market at weekends, good dart service into town.
The main street has its fair share of dodgy characters but what town doesn't.
Dunno about property capital growth but I would try and pick a "named" area if possible for best capital growth e.g. Sandycove