I have also had success asking at check-in about an upgrade fee. I have been successful more often than not and every time, the upgrade has been $100 per night. Since this is usually less than the website difference between club and non-club, it's worth asking.
As for the value, there is absolutely no question, IMHO, that club is almost always worth it, even at the published rates. With two in the room, you really only have to do breakfast and a couple of drinks in the evening to make up the difference. If you have a day or two where you're just hanging at the pool, you can easily eat every meal there and save a bundle.