Upgraded to clasps after a zipper burst in transit. The new cases came with TSA combo locks built in. Agree that locks keep the opportunists out - from my perspective for that reason alone they are worth it. In terms of locks attracting attention - possibly if the suitcase just has the zipper type but so many suitcases have TSA locks built into them these days that I suggest it is neither here nor there as a generator of attention. I would suggest that the absence of any form of lock would be an attraction to the opportunists.
As an aside, I did pick up the wrong piece of luggage once (brand new suitcase that I hadn't had time to customise) got it home and went to open it - combination lock stopped me and made me realise without intruding into the owners personal space. For me, no question about having a lock now.
As a further aside, for those that are of the view that they don't travel with anything of value - value is a perception - I have worked in places where people steal toilet paper off the roll in cubicles and in this environment even used clothing (including shoes) can be high value commodities - don't underestimate the potential value and more importantly don't underestimate the potential inconvenience if you were to lose it. Try buying large clothing, socks and even underwear in some countries and you will pull your hair out (if you are not already bald!).