I've 'dumped' the return portion of several tickets over the years, but bear in mind that some airlines DO keep records and there is a possibility that on the next flight you may get pulled despite having a valid ticket.
It doesn't happen often, but it does happen. Not trying to scare you, just passing the info. Personally, I would buy whatever is cheapest and dump the return. As long as you don't make a habit of it with the same airline, you are likely fine.