Extreme vibration can cause problems, but not like it used to. A motorcycle needs to vibrate some. That's part of the experience. Look at Harley. They vibrate like crazy, but still hold together. Nobody is likely to be afraid to take their new Harley on the freeway. You can take a brand new 883 Sportster (which costs very little more than the Enfield) on the freeway, open it up, and cruise all day long without worries. You might not be able to handle it, but the bike can. Harleys don't require any special maintenance, in fact they are one of the lowest maintenance bikes there is, with their hydraulic valves, spin on oil filter, and belt drive. And just like a used Bonneville, you can get a nice used Sportster for way less than a new Royal Enfield. The Enfield does have looks, I won't argue with that. But to me the looks alone are not worth $8000.
2002 Vulcan 750 (engine out, slowly being disassembled) 2013 Royal Enfield B5
2001 XT225, 2009 Genuine Stella
2012 Zuma 125, 1980 Puch moped