handlea, welcome to FT. Your question is a good one and is perennially debated around here. The answer is, of course, it depends. You can search (perhaps "value" would be a good search term?) and turn up lots of discussion. The real question is, is it worth it to you? If you don't fly premium cabins, then 1.5 cents/mile isn't too bad. If it takes you a long time to accumulate the miles for a trip, or conversely you have so many miles you'll never run out, it's not a bad idea either.
Personally, I probably wouldn't do it since I use the majority of my miles for upgrades (SFO/LAX-JFK mostly), but literally, your mileage may vary.
Michael