This is a great point. I originally started this quest looking at a .338 Marlin Express because I wanted "new and cool". However it was quickly apparent when I really looked into that cartridge there wasn't much of a range of loads there to experiment with. Plus cartridge history is littered with interesting cartridges that fail to catch on and I wanted something that will last as I don't spend a tremendous amount on guns (as much as I'd like to!).
I have to admit I was initially against the .30-30 because it was "old" but some serious research quickly proved to me what a great cartridge it is.
If I got rid of my one .40S&W, then I every other cartridge I own a gun in would have been originally designed more than 100 years ago.... hrmm....