My wife and I have been flying all over the world for years, always in the economy section. Buying a business class ticket straight away always seems to be at least triple the price of economy which I still can't justify. The other day we flew from SF to Copenhagen in business class after discovering optiontown.com and upgrading for about $450 each. What a treat. Unfortunately optiontown.com only works with a few airlines which we don't fly very often. Are there any other ways to purchase business class upgrades at a discount?

Using a miles credit card makes sense and my business charges nearly $50K/month on credit cards, but I use a 1.5% cash back card now which translates into about $750/month. Would I accumulate miles worth more than that? The other thing about miles credit cards is they're associated with a particular airline and we fly with various airlines (although we do fly United a lot).