Guess your friend doesn't realize that you really do get what you pay for! Sometimes spending just a bit more can get you alot more.
As Warren Buffet says, "Price is what you pay. Value is what you get."
Your friend is more concerned about pricing than about value.
The one good thing about cruising is that there's definitely something out there for everyone. But I think the best part about cruising is trying them all until you find the one that's best for you. I can't imagine only trying one cruise line and never trying any of the others - that would be a shame. We've been on 11 cruise lines and 45 cruises, and I can honestly say that we have thoroughly loved every one of them. Like you, we don't sweat the small stuff. And yes, some have obviously been better than others, but even the worst was really not that bad.
BTW, if you like RCCL, give Princess a try. Or if you're a bit older, you might even want to try Holland or Celebrity. Not as good for kids as RCCL, but the food is much better.